Rolling bearing and bearing apparatus

ABSTRACT

In a bearing apparatus which are composed of two bearings each including a crown-shaped retainer and also in which a lubricant is filled into raceways formed in the two bearings, not only a preload is applied from the retainer pocket opening side end face of an inner ring but also a preload is applied from the retainer pocket counter-opening side end face of an outer ring.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an improvement in a bearing apparatus for use in a spindle (which is also referred to as SPM) which is applied to, for example, a hard disk drive apparatus (which is also referred to as HDD) and a video cassette recorder (which is also referred to as VCR).

[0002] The present invention relates to a rolling bearing and a bearing apparatus for use in a small-sized motor which is used mainly in information equipment and home appliances.

[0003] The present invention relates to an improvement in a bearing apparatus for use in various kinds of rotary equipment such as a spindle motor provided in a hard disk drive apparatus (which is also referred to as an HDD) and a video cassette recorder (which is also referred to as a VCR).

[0004] The present invention relates to a reduction not only in the vibrations and noises but also in the dynamic friction torque of the bearing apparatus which is used to support a motor shaft such as a spindle provided in a hard disk drive apparatus (which is also referred to as HDD) and a drum spindle provided in a video cassette recorder (which is also referred to as VCR).

[0005] The present invention relates to a ball bearing and a bearing apparatus for a small-sized motor which are used in a hard disk drive apparatus (which is also referred to as an HDD), a video cassette recorder (which is also referred to as a VCR), or a laser beam printer (which is also referred to as an LBP).

[0006] The present invention relates to a reduction in the dynamic friction torque of a bearing apparatus used to support a motor shaft.

[0007] Conventionally, the above bearing apparatus, as shown in FIG. 44, comprises a pair of bearings 100 and 100 combined together. The combining direction of the two bearings is not fixed specifically but, generally, the opening sides 201 of the respective retainers 200 of the two bearings 100 and 100, in which dust is easy to occur, are disposed opposed to each other, whereby the bearings 100 and 100 are disposed as a bearing unit which can reduce the generation of dust to the outside of the bearing unit. In FIG. 44, reference character 300 designates a shaft and 400 stands for a spacer which is interposed between the two bearings 100 and 100.

[0008] Also, as shown in FIG. 45, there is generally known a bearing with a shaft in which a double-row raceways 301 and 301 are formed directly in the shaft 300 and a spring 500 is interposed between two outer rings 101 and 101. In this structure as well, the crown-shaped retainers 200 are incorporated in such a direction that, similarly to the structure shown in FIG. 44, their respective retainer opening sides 202 are opposed to each other. In FIGS. 29 and 30, arrow marks respectively show preload directions. Today, in order to enhance the oscillation resistance (which is also referred to as fretting resistance) of the product (bearing) in transit, a lubricant to be filled into the bearing, generally, is filled into the raceways of the bearing, instead of a related method in which the lubricant is filled onto the retainer.

[0009] However, when the bearing apparatus of this type is rotated, since the lubricant (a grease as a representative example) is filled in the raceways, the rotation torque of the bearing apparatus and variations in such rotation torque are large, and the vibrations of the bearing apparatus not synchronous with the rotation of the bearing apparatus (which is also referred to as NRRO) are also large.

[0010] Now, FIG. 46 is an enlarged view of a retainer to be incorporated into the related bearing apparatus shown in FIG. 45, showing how the retainer is incorporated. That is, in such related structure, grease G collecting in the counter-contact-angle side of the outer ring 101 is involved with the rotational movement of a ball 600 and is thereby moved in the rotation (about its own axis) direction of the ball 600, the grease G is scraped by the crown-shaped retainer 200, the thus scraped grease G collects into the outside diameter portion of the retainer end face side (pocket counter-opening side) 202 to provide a collection of grease, and this grease collection is contacted with grease G on the outer ring 101 side to thereby generate large resistance, so that the rotation torque of the bearing apparatus increases. Also, the grease G, which has been scraped once, is easy to be involved with the rotational movement of the ball 600, which causes the rotation torque to be unstable and large.

[0011] By the way, In the case of an HDD spindle motor for use in information equipment, as shown in FIGS. 47 and 48, a hub 730 is rotatably supported on the periphery of a shaft 720 by a pair of rolling bearings 770 and 770 disposed with a space between them One end of the shaft 720 is fixed to the central portion of a fixing plate 740 which is referred to as a housing. The rolling bearings 770 and 770 are interposed between the outer peripheral surfaces of the base end portion (in FIG. 47, the lower end portion) and leading end portion (in FIG. 47, the upper end portion) of the shaft 720, so that the hub 730 can be rotated on the periphery of the shaft 720. To the portion of the middle portion outer peripheral surface of the shaft 720 that is held by the pair of rolling bearings 770 and 770, there is fixed a stator 750; to the portion of the middle portion inner peripheral surface of the hub 730 that is opposed to the outer peripheral surface of the stator 750, there is fixed a rotor 760; and, the stator 750 and rotor 760 cooperate together in constituting an electric motor 770 which is used to drive or rotate the hub 730. Also, to the outer peripheral surface of the hub 730, there are fixed a plurality of hard disks 780, 780. By the way, reference character 790, 790 respectively designate heads for reading records from the hard disks 780, 780 and writing records into the hard disks 780, 780.

[0012] On the other hand, the two rolling bearings 770 and 770 respectively comprise inner rings 701 and 701 having inner raceways 701 a and 701 a formed in the outer peripheral surfaces thereof, outer rings 702 and 702 having outer raceways 702 a and 702 a formed in the inner outer peripheral surfaces thereof, a plurality of rolling elements 703, 703 rotatably interposed between the inner raceways 701 a, 701 a and outer raceways 702 a, 702 a, and crown-shaped retainers 704 made of synthetic resin.

[0013] Also, between the outer peripheral surfaces of the axial-direction two end portions of the respective inner rings 701 and 701 and the inner peripheral surfaces of the two end portions of the respective outer rings 702 and 702, there are interposed a pair of seal rings 705 and 705 each of which is formed in a circular ring to thereby close spaces between the inner ring and outer ring peripheral surfaces. The upper and lower bearings are combined together in such a manner that, in order to reduce dust generation to the outside of the bearings, the opening sides 704 a and 704 a of the crown-shaped retainers 704 and 704 of the bearings are opposed to each other.

[0014] Further, into spaces 706 defined by and between the pair of seal rings 705 and 705, there is filled grease 107 and 107 from the one-end opening sides (in FIG. 47, in the case of the upper rolling bearing 770 the lower end opening side; and, also in FIG. 47, in the case of the lower rolling bearing 770, the upper end opening side) of the respective spaces 706 and 706. Of the pair of seal rings 705 and 705, at least the seal ring 705 on the grease 107 filling side is to be mounted into a given portion after completion of the grease filling operation.

[0015] After the seal rings 705 and 705 are mounted, the seal rings 705 and 705 prevent the grease 107 filled in the respective spaces 706 and 706 from leaking therefrom to the outside.

[0016] However, in the above related bearing apparatus, there are still found problems to be solved: that is, when it is rotated, the rotation torque thereof and variations in the rotation torque are large as well as vibrations not synchronous with the rotation of the bearing apparatus (which is also referred to as NRRO) are also large.

[0017] In view of the above, in order to solve the above problems found in the related bearing apparatus, the present inventors have previously proposed a bearing apparatus (Japanese Patent Application 2001-209387) structured such that a bearing incorporating a crown-shaped retainer is fixed to a shaft, wherein a preload is applied not only to the retainer opening side of the inner ring of the bearing but also to the retainer counter-opening side of the outer ring of the bearing. In this case, it is required that the opening and counter-opening sides of the retainer incorporated into the bearing can be distinguished from each other simply and positively from the outside. Especially, in the case of a related bearing with seal plates respectively mounted on the two ends thereof, the opening and counter-opening sides of the retainer of the bearing, that is, the incorporating direction of the retainer cannot be distinguished from each other.

[0018] By the way, for a motor shaft which is used to drive a hard disk apparatus or a floppy disk apparatus for use in a personal computer and a word processor, there is used a ball bearing having a small diameter. In the case of a ball bearing, as a type for guiding a retainer made of synthetic resin, there are known a rolling element guide type for guiding a retainer using a rolling element (a ball) and an inner ring or outer ring guide type for guiding a retainer using an inner ring or an outer ring. In either of the guide types, as the time passes, the quantity of a lubricant (grease, or an oil component) filled into the pocket of the retainer decreases, so that the frictional torque of the bearing gradually decreases and becomes almost constant.

[0019] As the shape of the pocket of the retainer for holding a ball, there are known two kinds of shapes: that is, as shown in FIG. 49 as well as in FIG. 50 which is an enlarged section view taken along the line VI-VI shown in FIG. 49, one type of retainer pocket shape is such that the inner wall of the pocket 840P of a retainer 840 for holding a ball 830 interposed between an outer ring 810 and an inner ring 820 has a flat cylindrical surface; and, as shown in FIG. 51 as well as in FIG. 52 which is an enlarged section view taken along the line VIII-VIII shown in FIG. 51, the other type of retainer pocket shape is such that the inner wall of the pocket 841P of a retainer 841 interposed between an outer ring 810 and an inner ring 820 has a spherical surface. And, most of the retainers of an inner ring or outer ring guide type include a cylindrical-shaped pocket; and, most of the retainers of a rolling element guide type include a spherical-shaped pocket. Also, depending on the situation, there may be taken means in which, as disclosed in JP-A-9-317774, there are formed fine undulations (raised and recessed portions) on the sliding surfaces of these retainers used in the bearings to thereby enhance the lubricating property of the retainers.

[0020] On the other hand, when these bearings are used in the above-mentioned motor, in order to enhance the rotation accuracy thereof, generally, two bearings are combined together as a pair and a given preload is given to the respective bearings.

[0021] As described above, in the case of the ball bearing, preferably, at the time when the quantity of the lubricant filled into the pocket of the retainer gradually decreases from the beginning as the time passes, the ball bearing may be stabilized and the frictional torque of the ball bearing may be constant.

[0022] However, in a retainer of an inner ring 820 (or outer ring 810) guide type including a cylindrical-shaped pocket 840P shown in FIGS. 49 and 50, most of the lubricants circulate in the order of ball surface-raceway surface-pocket surface-ball surface and are left within the pocket. Due to this, the friction torque of the bearing is large when compared with a bearing of a rolling element guide type including a spherical-shaped retainer pocket, which raises a problem to be solved. That is, in the case of a bearing including a retainer of a race guide type including a cylindrical-shaped pocket, since a ball is contacted with the center of the pocket, there does not occur a scraping operation for scraping away the lubricants and thus, even as the time passes, in most cases, the torque of the bearing does not lower.

[0023] On the other hand, in the retainer 841 of a rolling element guide type shown in FIGS. 51 and 52, extra lubricants G sticking to the surface of the ball 830 are scraped away by the edge portion of the spherical-surface pocket 841P and are stuck to the inner or outer peripheral surface of the retainer to thereby have no influence on the torque of the bearing; and, the viscous resistance of the lubricant with respect to the ball and race contact portion decreases as the rotation time passes and the reduction of the torque also advances.

[0024] And, in case where the scraping operation advances excessively due to the high-speed rotation, cutting of an oil film occurs in the pocket edge portion and ball surface to cause poor lubrication and, due to the poor lubrication, there are produced strange sounds. Also, in order to prevent such poor lubrication, in case where the sliding surface of the retainer is set not flat or smooth but is set so as to have desired roughness to thereby form lubricating oil standing portions and thus prevent cutting of the oil film, the friction of the retainer can be controlled for a long period of time. However, in the case of a bearing using such retainer as well, similarly to the above-mentioned retainer including a cylindrical-shaped pocket, there is found a problem that the friction torque of the bearing is large.

[0025] By the way, Conventionally, as means for supporting various rotary parts, for example, there is widely used such a ball bearing as disclosed in JP-A-10-159855 (see FIG. 54).

[0026] This ball bearing comprises an outer ring 3 having an outer raceway formed in the inner peripheral surface thereof, an inner ring 2 having an inner raceway formed in the outer peripheral surface thereof, a crown-shaped retainer 5 interposed between the outer and inner rings 3 and 2 in such a manner that it can be rotated with respect to the outer and inner rings 3 and 2, and a plurality of balls 4 rotatably held in a plurality of pockets 5 d formed in the crown-shaped retainer 5. And, the outer peripheral edges 9 a of two circular-ring-shaped shield plates 9 are respectively secured to the inner peripheral surfaces of the two end portions of the outer ring 3. That is, the two shield plates 9 not only prevent grease existing in the above-mentioned ball installation portions from leaking to the outside but also prevent dust floating in the outside from flowing into the ball installation portions.

[0027] As described above, the plurality of balls 4 are rotatably held by the retainer 5; and, as the retainer 5, for example, as shown in FIGS. 53A and 53B, there is conventionally used a retainer which is referred to as a crown-shaped retainer. This retainer 5 has the same number of spherically-concave-surface pockets 5 d as the balls 4 in order to hold the balls 4 in a freely rollable manner, while the radius of curvature of the spherically concave surface of the retainer pocket is set slightly larger than the radius of curvature of each of the balls 4.

[0028] Also, when the bearing of this type is used to support various rotary apparatus, generally, two bearings 1 and 1 of this type are used in combination.

[0029] However, in the above-mentioned related bearing, there are still found the following problems to be solved.

[0030] That is, recently, as the rotation speed of the rotary apparatus increases, there increases the need for a reduction in the noises and vibrations of the bearing as well as for a reduction in the dynamic friction torque of the bearing. However, the related bearing apparatus has become more and more difficult to meet such reduction needs. That is, to reduce the noises and vibrations, the pocket diameter of the retainer 5 may be reduced to reduce the play of the retainer 5 with respect to the ball 4, thereby controlling the movement of the retainer 5. However, in case where the play (clearance) of the retainer 5 is reduced, the shearing resistance of lubricants existing between the retainer pockets 5 d and balls 4 increases, with the result that the dynamic friction torque of the bearing apparatus increases.

[0031] By the way, conventionally, a ball bearing to be incorporated into the above-mentioned HDD, VCR or LBP, for example, as shown in FIG. 44, is composed of a pair of bearings 100 and 100 combined together; and, the combining direction of the two bearings 100 and 100 is not fixed to any specific direction but, generally, the two bearings 100 and 100 are disposed in such a manner that the pocket opening sides 201 of the respective retainers 200 of the two bearings 100 and 100 are opposed to each other, thereby being able to reduce generation of dust to the outside of the bearings 100 as a bearing unit.

[0032] Also, today, in order to enhance the oscillation resistance (which is also referred to as the fretting resistance) of the product (ball bearing) in transit, a lubricant to be filled into the ball bearing, generally, is filled into raceways formed in the two bearings, differently from a related lubricant filling system in which the lubricant is filled onto the retainers of the two bearings. By the way, in FIG. 44, reference character 300 designates a shaft and 400 stands for a spacer which is inserted between the two bearings 100 and 100.

[0033] However, in the bearing apparatus of this type, there is still found a problem: that is, when it is rotated, since the lubricant is sealed in the grooves of the two bearings, the rotation torque of the apparatus and the variations of the rotation torque are large and also vibrations not synchronous with the rotation (NRRO) of the apparatus are large.

[0034] By the way, to support various rotary parts, conventionally, there is widely used a ball bearing which is disclosed, for example, in JP-A-10-159855 (see FIG. 54).

[0035] This ball bearing comprises an outer ring 3 having an outer raceway formed in the inner peripheral surface thereof, an inner ring 2 having an inner raceway formed in the outer peripheral surface thereof, a crown-shaped retainer 5 interposed between the outer and inner rings 3 and 2 in such a manner that it can be rotated with respect to the outer and inner rings 3 and 2, and a plurality of balls 4 respectively rotatably held in a plurality of pockets 5 d formed in the crown-shaped retainer 5.

[0036] To the inner peripheral surfaces of the two end portions of the outer ring 3, there are secured the outer peripheral edges 9 a and 9 a of their associated circular-ring-shaped shield plates 9 and 9, respectively; and, the two shield plates 9 and 9 prevent grease existing in the above-mentioned ball installation portions from leaking to the outside or prevent dust floating in the outside from flowing into the ball installation portions.

[0037] And, as described above, the plurality of balls 4 are rotatably held by the retainer 5 and, as the retainer 5, conventionally, there is used such a crown-shaped retainer as shown in FIG. 53A.

[0038] This retainer 5 includes the same number of spherically concave surfaces as the balls 4 so as to hold the balls 4 rotatably, while the radius of curvature of the spherically concave surface is set slightly larger than the radius of curvature of the ball 4.

[0039] By the way, when this bearing is used to support various rotary apparatus, generally, the two bearings land 1 are combined together.

[0040] Also, when the two bearings are used under the high-speed rotation condition, in order to restrict the mechanical slippage of the interior portion of the bearing, it has been considered effective to reduce a contact angle at which the balls and the raceway surfaces of the races of the bearing are contacted with each other.

[0041] However, recently, as the rotation speed of the various rotary apparatus increases, there has been increased the need for a reduction in the dynamic friction torque of the bearing; that is, simply by reducing the contact angle in the above-described manner, the dynamic friction torque of the bearing caused by the high-speed rotation of the bearing can not be restricted sufficiently.

[0042] Specifically, the high-speed rotation of the bearing causes the grease existing in the interior of the bearing to move much and, especially, the grease moved to the inside diameter side of the outer ring due to a centrifugal force is stirred between the outer ring inside diameter side and the outside diameter portion of the retainer, thereby increasing stirring resistance or shearing resistance, with the result that the dynamic friction torque of the bearing is increased.

SUMMARY OF THE INVENTION

[0043] The present invention aims at eliminating the drawbacks found in the above-mentioned related bearing apparatus. Accordingly, it is a first object of the present invention to provide a bearing apparatus which not only is small in rotation torque and variations in such rotation torque but also is high in rotation accuracy.

[0044] The present invention aims at eliminating the drawbacks found in the above-mentioned related bearing and bearing apparatus. Accordingly, it is a second object of the present invention to provide a rolling bearing in which the incorporating direction of a retainer can be distinguished easily from the outside and the assembling direction of the bearing can be controlled positively according to the incorporating direction of the retainer. Also, it is another object of the present invention to provide a bearing apparatus which is small in rotation torque and variations in the rotation torque as well as is high in rotation accuracy.

[0045] The present invention aims at eliminating the drawbacks found in the above-mentioned related bearing apparatus. Accordingly, it is a third object of the present invention to provide a bearing apparatus which not only can maintain the proper quantity of a lubricant to thereby stabilize the friction torque of the bearing but also can control an increase in the temperature thereof and the friction thereof.

[0046] The present invention aims at eliminating the drawbacks found in the related bearing apparatus. Accordingly, it is a fourth object of the present invention to provide a bearing apparatus which can satisfy the need for reduction in the noises and vibrations thereof as well as for a reduction in the dynamic friction torque thereof.

[0047] The present invention aims at solving the above problem found in the related bearing apparatus. Accordingly, it is a fifth object of the present invention to provide a ball bearing and a bearing apparatus which not only are low in rotation torque and variations thereof but also are high in rotation accuracy.

[0048] The present invention aims at eliminating the drawbacks found in the above-mentioned related bearing apparatus. Accordingly, it is a sixth object of the present invention to provide a bearing apparatus which can satisfy the need for a reduction in the dynamic friction torque thereof.

[0049] In attaining the first object, according to a first aspect of the present invention, there is provided a bearing apparatus comprising a bearing fixed to a shaft, the bearing including: an outer ring having an outer raceway formed in an inner peripheral surface thereof; an inner ring having an inner raceway formed in an outer peripheral surface thereof; a crown-shaped retainer interposed between the outer and inner rings so as to be rotated with respect to the outer and inner rings; and a plurality of balls rotatably held in a plurality of pockets formed in the crown-shaped retainer, wherein a preload is applied to an retainer opening side of the inner ring of the bearing and an retainer counter-opening side of the outer ring of the bearing. That is, the present bearing apparatus is used in a state where a contact angle does not provide an angle of zero, while a contact point between the inner ring and ball is situated in the inner raceway surface on the retainer pocket opening side, and a contact point between the inner ring and ball is situated in the outer raceway surface on the retainer pocket counter-opening side.

[0050] And, according to a second aspect of the present invention, there is provided a bearing apparatus comprising two bearings fixed to a shaft, each bearing including: an outer ring having an outer raceway formed in an inner peripheral surface thereof; an inner ring having an inner raceway formed in an outer peripheral surface thereof; a crown-shaped retainer interposed between the outer and inner rings so as to be rotated with respect to the outer and inner rings; and a plurality of balls rotatably held in a plurality of pockets formed in the crown-shaped retainer, wherein a preload is applied to the retainer opening sides of the respective inner rings of the two bearings and the retainer counter-opening sides of the respective outer rings of the two bearings. Also, a bearing apparatus as set forth in the second aspect of the present invention, wherein the respective retainers of the two bearings are incorporated in such a manner that the pocket counter-opening sides of the retainers are opposed to each other. Further, a bearing apparatus as set forth in the second aspect of the present invention, wherein the respective retainers of the two bearings are incorporated in such a manner that the pocket opening sides of the retainers are opposed to each other.

[0051] According to a third aspect of the present invention, there is provided a bearing apparatus comprising two bearings structured such that a preload is applied to the respective outer rings of the two bearings in a direction to separate the outer rings in the two rows from each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that their respective pocket counter-opening sides are opposed to each other. Also, in the present bearing apparatus, there is interposed a spring between the respective outer rings of the two bearings.

[0052] According to a fourth aspect of the present invention, there is provided a bearing apparatus comprising two bearings structured such that a preload is applied to respective outer rings of the two bearings by a spring interposed between the respective outer rings in a direction to separate the outer rings from each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket counter-opening sides of the retainer are opposed to each other.

[0053] According to a fifth aspect of the present invention, there is provided a bearing apparatus comprising two bearings structured such that a preload is applied to respective outer rings of the two bearings in a direction to approach the outer rings each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket opening sides of the retainers are opposed to each other.

[0054] According to a sixth aspect of the present invention, there is provided a bearing apparatus comprising two bearings structured such that a preload is applied to respective inner rings of the two bearings in a direction to approach the inner rings each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket counter-opening sides of the retainers are opposed to each other. Also, there is provided a bearing apparatus comprising two bearings structured such that a preload is applied to respective inner rings of the two bearings by a spring interposed between the respective inner rings in a direction to separate the inner rings from each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket opening sides of the retainers are opposed to each other.

[0055] In the above-mentioned double-row-type bearing apparatus, a bearing apparatus as set forth in the fifth to eighth aspects of the present invention, further comprising a shaft fixing the two bearings, wherein the shaft includes a double row raceway so as to receive rolling elements of the two bearings; or, the inner rings may be fixed to the shaft; or, a spring may be interposed between the outer rings of the two bearings; or, the bearings further comprises a shaft fixed to the bearing and an inner ring, wherein the shaft includes a raceway formed in one side thereof so as to receive rolling elements of one of the two bearings, whereas the inner ring is fixed to the other side of the shaft so as to receive rolling elements of the other of the two bearings. Also, in the double-row-type bearing apparatus, a bearing apparatus as set forth in the fifth to eighth aspects of the present invention, wherein a raceway for balls is formed at least in a portion of the shaft or a housing.

[0056] Also, a bearing apparatus as set forth in the first aspect of the present invention, wherein the bearing apparatus is of an outer ring rotation type or an inner ring rotation type.

[0057] Further, in all or some of the above-mentioned bearing apparatus, a bearing apparatus as set forth in the first aspect of the present invention, wherein an indicating arrangement allowing the incorporating direction of the retainer to be distinguished is provided on at least one of one end face and the other end face of the bearing apparatus in the axial direction thereof.

[0058] In attaining the above second objects, according to a seventh aspect of the present invention, there is provided a rolling bearing comprising: an inner ring having an inner raceway formed in an outer peripheral surface thereof; an outer ring having an outer raceway formed in an inner peripheral surface thereof; a plurality of rolling elements rotatably interposed between the inner raceway and the outer raceway; a crown-shaped retainer for holding the rolling elements at regular intervals; and a seal ring interposed between the inner and outer rings for sealing grease or lubricating oil filled into a bearing space or for preventing dust from being generated to the outside, wherein an indicating arrangement allowing the incorporating direction of the retainer to be distinguished is provided on one end face and the other end face of the bearing in the axial direction thereof. And, according to a eighth aspect of the present invention, in a rolling bearing as set forth in the seventh aspect of the present invention, the indicating arrangement may be a mark provided on either of the one end face or the other end face of the bearing in the axial direction thereof.

[0059] Also, according to a ninth aspect of the present invention, in a rolling bearing as set forth in the eighth aspect of the present invention, the mark includes a toothing. Further, according to a tenth aspect of the present invention, in a rolling bearing as set forth in the seventh aspect of the present invention, the indicating arrangement may be seal ring disposed on either of the one end face or the other end face of the bearing in the axial direction thereof. And, according to a eleventh aspect of the present invention, in a rolling bearing as set forth in the seventh aspect of the present invention, the indicating arrangements may be seal rings which are respectively disposed on both of the one end face and the other end face of the bearing in the axial direction thereof and differ in color from each other.

[0060] Also, according to a twelfth aspect of the present invention, there is provided a bearing apparatus in which a bearing as set forth in any one of the seventh to five aspects of the present invention, may be fixed to a shaft and a preload is applied to a retainer opening side of the inner ring and a retainer counter-opening side of the outer ring.

[0061] In attaining the above third object, according to an eighth aspect of the present invention, there is provided a bearing apparatus, as set forth in the first aspect of the present invention, a bearing apparatus structured as set forth in the first aspect of the present invention, wherein crown-shaped retainer has at least a rolling element sliding contact surface formed as a rough surface. Also, there is provided a bearing apparatus, as set forth in the second aspect of the present invention, the crown-shaped retainers have at least a rolling element sliding contact surface formed as a rough surface.

[0062] In the above bearing apparatus, there can also be employed a structure that two bearings, each consisting of the above-mentioned bearing, are combined together as a pair. Also, in the bearing apparatus composed of two bearings combined together as a pair, not only in a case where the respective retainers of the two bearings are incorporated in such a manner that the pocket counter-opening sides thereof are disposed opposed to each other, but also in a case where the respective retainers of the two bearings are incorporated in such a manner that the pocket opening sides thereof are disposed opposed to each other, a preload is applied not only to the retainer opening sides of the respective inner rings of the two bearings but also to the retainer counter-opening sides of the respective outer rings of the two bearings.

[0063] In attaining the above fourth object, according to a ninth aspect of the present invention, there is provided a bearing apparatus, as set forth in the first aspect of the present invention, a ratio Dp/Dw of a pocket diameter (Dp) of the retainer to a diameter of the ball (Dw) is set such that 1.050>Dp/Dw>1.005.

[0064] Also, according to a tenth aspect of the present invention, there is provided a bearing, as set forth in the scond aspect of the present invention, a ratio Dp/Dw of a pocket diameter (Dp) of the retainer to the diameter of the ball (Dw) is set such that 1.050>Dp/Dw>1.005. And, the retainers of the two ball bearings are incorporated in such a manner that the pocket counter-opening sides of the two retainers are disposed opposed to each other or the pocket opening sides thereof are disposed opposed to each other.

[0065] In attaining the above fifth object, according to a eleventh aspect of the present invention, there is provided a ball bearing, comprising: an inner ring having an inner raceway formed in an outer peripheral surface thereof; an outer ring having an outer raceway formed in an inner peripheral surface thereof; a plurality of balls rotatably incorporated between the inner raceway and the outer raceway; and a crown-shaped retainer for holding the balls at regular intervals, wherein a preload is applied to a pocket opening side of the inner ring of the retainer and a pocket counter-opening side of the outer ring of the retainer, and a pawl height T of the retainer is set 20% or less of the diameter Da of the ball (T≦20%×Da) with a shoulder position of the raceway of the outer ring as the standard. Also, according to a twelfth aspect of the present invention, in a ball bearing as set forth in the eleventh aspect of the present invention, an indicating arrangement allowing the incorporating direction of the retainer to be distinguished is provided on the two end faces of the ball bearing in the axial direction thereof. Further, according to a thirteenth aspect of the present invention, there is provided a bearing apparatus, wherein a ball bearing as set forth in the eleventh or twelfth aspect of the present invention is incorporated into a shaft.

[0066] In attaining the above sixth object, according to a fourteenth aspect of the present invention, there is provided a bearing apparatus, as set forth in the first aspect of the present invention, an initial contact angle between the ball and raceway surface of the raceway is set at an angle of 50 or more.

[0067] Also, in case where a bearing apparatus comprises two ball bearings respectively fixed to a shaft, two bearings may be fixed to a shaft and the retainers of the two ball bearings are incorporated in such a manner that respective pocket counter-opening sides of the retainers are opposed to each other. Alternatively, two ball bearings may be fixed to a shaft and the retainers of the two ball bearings are incorporated in such a manner that respective pocket opening sides of the retainer are opposed to each other.

[0068] Further, two seal plates may be respectively disposed on the two end portions of the bearing in the axial direction thereof, and indicating arrangements allowing the incorporating direction of the retainer to be distinguished are provided on the two end portions of the bearing in the axial direction thereof and differ in color from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069]FIG. 1 is a schematic section view of a first embodiment of a bearing apparatus according to the present invention;

[0070]FIG. 2 is a schematic enlarged view of the retainer incorporating direction portion of the first embodiment;

[0071]FIG. 3 is a schematic section view of a second embodiment of a bearing apparatus according to the present invention;

[0072]FIG. 4 is a schematic section view of a third embodiment of a bearing apparatus according to the present invention;

[0073]FIG. 5 is a schematic enlarged view of the retainer incorporating direction portion of the third embodiment;

[0074]FIG. 6 is a schematic section view of a fourth embodiment of a bearing apparatus according to the present invention;

[0075]FIG. 7 is a schematic section view of a fifth embodiment of a bearing apparatus according to the present invention;

[0076]FIG. 8 is a schematic section view of a sixth embodiment of a bearing apparatus according to the present invention;

[0077]FIG. 9 is a schematic section view of a seventh embodiment of a bearing apparatus according to the present invention;

[0078]FIG. 10 is a schematic section view of an eighth embodiment of a bearing apparatus according to the present invention;

[0079]FIG. 11 is a schematic section view of a ninth embodiment of a bearing apparatus according to the present invention;

[0080]FIG. 12 is a schematic section view of a tenth embodiment of a bearing apparatus according to the present invention;

[0081]FIG. 13 is a schematic section view of an eleventh embodiment of a bearing apparatus according to the present invention;

[0082]FIG. 14A is a schematic enlarged view of the retainer incorporating direction portion of the eleventh embodiment; and, FIG. 14B is a partially enlarged view of the retainer pawl portion, showing a state thereof when viewed from top;

[0083]FIG. 15 is a schematic view of a bearing apparatus according to the eleventh embodiment, showing its assembling method;

[0084]FIG. 16 is a schematic section view of a twelfth embodiment of a bearing apparatus according to the present invention;

[0085]FIG. 17 is a schematic section view of a thirteenth embodiment of a bearing apparatus according to the present invention;

[0086]FIG. 18 is a schematic section view of a fourteenth embodiment of a bearing apparatus according to the present invention;

[0087]FIG. 19 is a schematic section view of a fifteenth embodiment of a bearing apparatus according to the present invention;

[0088]FIG. 20 is a schematic section view of a sixteenth embodiment of a bearing apparatus according to the present invention;

[0089]FIG. 21 is a schematic section view of a seventeenth embodiment of a bearing apparatus according to the present invention;

[0090]FIG. 22 is a schematic section view of an eighteenth embodiment of a bearing apparatus according to the present invention;

[0091]FIG. 23 is a schematic section view of a nineteenth embodiment of a bearing apparatus according to the present invention;

[0092]FIGS. 24A and 24B show a distinctive arrangement allowing a retainer incorporating direction to be distinguished; specifically, FIG. 24A is a schematic section view of a bearing apparatus according to the present invention, and FIG. 24B is a front view thereof;

[0093]FIG. 25 is a schematically longitudinal section view of a twenty-first embodiment of a bearing apparatus according to the present invention;

[0094]FIG. 26 is a schematically longitudinal section view of a twenty-second embodiment of a bearing apparatus according to the present invention;

[0095]FIGS. 27A and 27B are schematic section views of structures on which a first test was conducted in order to observe the movement of grease existing in the interior of a bearing; specifically, FIG. 27A shows a structure according to the prior art, and FIG. 27B shows a structure according to the present invention;

[0096]FIG. 28 is a graphical representation of the results of the first test for confirmation of the effects of the present invention;

[0097]FIGS. 29A and 29B show the results of the second test conducted in order to confirm the effects of a related bearing apparatus (specifically, FIG. 29A shows time series variations in the torque of the related bearing apparatus; and, FIG. 29B shows time series variations in NRRO thereof);

[0098]FIGS. 30A and 30B show the results of a second test conducted in order to confirm the effects of the present invention (specifically, FIG. 30A shows time series variations in the torque of the bearing apparatus according to the present invention; and, FIG. 30B shows time series variations in NRRO thereof);

[0099]FIG. 31 is a schematic section view of an HDD/SPM apparatus;

[0100]FIG. 32 is a perspective view of an embodiment of a crown-shaped retainer to be incorporated into a bearing apparatus according to the present invention;

[0101]FIG. 33 is a graphical representation of the third test results;

[0102]FIG. 34 is a graphical representation of the results of a fourth test conducted to confirm the effects of the present invention and related comparison example;

[0103]FIG. 35A is a schematic view of a bearing, showing a preload direction according to the present invention (an A-direction preload shown in FIG. 34); and, FIG. 35B is a schematic view of a bearing, showing a preload direction according to the related comparison example (a B-direction preload shown in FIG. 34);

[0104]FIG. 36 is a partially sectional view of an embodiment of a ball bearing according to the present invention;

[0105]FIG. 37 is a perspective view of an embodiment of a crown-shaped retainer;

[0106]FIG. 38 shows the results of a fifth test conducted to confirm the effects of the present invention;

[0107]FIG. 39 is a schematic view of another embodiment of a retainer pawl portion;

[0108]FIG. 40 is a schematic section view of a twenty-ninth embodiment of a bearing apparatus according to the present invention;

[0109]FIG. 41 is a schematic section view of a thirtieth embodiment of a bearing apparatus according to the present invention;

[0110]FIG. 42 is a graphical representation of the results of a sixth test conducted to confirm the effects of the present invention;

[0111]FIGS. 43A and 43B are schematic views of a bearing, showing preload directions; specifically, FIG. 43A shows an A-direction preload, and FIG. 43B shows a B-direction preload;

[0112]FIG. 44 is a schematic section view of a related bearing apparatus;

[0113]FIG. 45 is a schematic section view of the related bearing apparatus;

[0114]FIG. 46 is a schematic enlarged view of the retainer incorporating direction portion of the related bearing apparatus shown in FIG. 45;

[0115]FIG. 47 is a longitudinal section view of a related bearing apparatus;

[0116]FIG. 48 is a longitudinal section view of the A portion shown in FIG. 47, while the A portion is enlargedly shown.

[0117]FIG. 49 is a section view of a portion of a related bearing apparatus incorporating therein a retainer having a flat cylindrical-shaped pocket;

[0118]FIG. 50 is a partially enlarged view of a section shown by the line VI-VI shown in FIG. 49;

[0119]FIG. 51 is a section view of a portion of a related bearing apparatus incorporating therein a retainer having a spherical-shaped pocket;

[0120]FIG. 52 is a partially enlarged view of a section shown by the line VIII-VIII shown in FIG. 51;

[0121]FIG. 53A is a perspective view of a crown-shaped retainer; and, FIG. 53B is a section view taken along the X arrow line shown in FIG. 53A; and,

[0122]FIG. 54 is a section view of a ball bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0123] Now, description will be given below of the preferred embodiments of a bearing apparatus according to the present invention with reference to the accompanying drawings. By the way, the embodiments illustrated herein are just an example of the present invention and thus the present invention is not limited to the illustrated embodiments at all. Also, the respective embodiments can be applied to either an outer ring rotation system or an inner ring rotation system.

[0124] First Embodiment

[0125] Now, FIG. 1 shows a first embodiment of a bearing apparatus according to the present invention. The present bearing apparatus comprises two rolling bearings 1 and 1, in which the two rolling bearings 1 and 1 are combined together in such a manner that the inner rings 2 and 2 of the two rolling bearings 1 and 1 are respectively fixed to the outer periphery of a shaft 6 and a preload (axial load) is applied to the two rolling bearings 1 and 1. Also, in the present embodiment, description will be given of a structure using two bearings as a pair; however, the present invention is not limited to such combination of two bearings.

[0126] The rolling bearing 1 is a ball bearing which comprises an inner ring having an inner raceway 2 a formed in the outer periphery thereof, an outer ring having an outer raceway 3 a formed in the outer periphery thereof, a plurality of rolling elements 4 to be interposed between the inner raceway 2 a and outer raceway 3 a, and a crown-shaped retainer 5 for holding the rolling elements 4 at regular intervals.

[0127] The crown-shaped retainer 5 comprises, for example, a ring-shaped main portion 5 c and a plurality of pockets 5 d formed in the axial-direction one surface of the main portion 5 c; and, more specifically, each of the pockets 5 d is interposed between a pair of pawls (which is also referred to as elastic pieces) 5 e disposed spaced from each other on the axial-direction one surface of the main portion 5 c.

[0128] Also, between the inner and outer rings 2 and 3 of each of the two bearings 1, there can be interposed a seal plate (in the present embodiment, a shield plate; and, a contact-type seal or a non-contact type seal can also be used) 9 can be used as the need arises. The structure of the seal plate 9 is not limited to any specific one but it can be changed variously without departing from the scope of the present invention. Also, in order to enhance the oscillation resistance of the product (bearing) in transit, a lubricant (a grease as a representative example) to be filled into the bearing 1 is to be filled into the raceways (that is, the inner raceway 2 a, outer raceway 3 a) of the bearing. Especially, according to the present invention, in the bearing apparatus comprising the two bearings 1 and 1 combined together and employing a lubricant filling system that a lubricant is to be filled into the raceways of the bearings, the rotation torque of the bearing apparatus can be reduced and the rotation accuracy of the bearing apparatus can be enhanced.

[0129] As described above, although the rolling bearing 1 is not limited to any specific structure but it employs an ordinary structure, the present embodiment has the following characteristic elements of the present invention: that is, the pocket counter-opening sides 5 b and 5 b of the respective retainers 5 and 5 of the two bearings 1 and 1 are disposed opposed to each other; and, a preload (axial load) is applied not only to the end faces 2 b and 2 b of the inner rings 2 and 2 situated on the retainer pocket opening sides 5 a and 5 a but also to the end faces 3 b and 3 b of the outer rings 3 and 3 situated on the retainer pocket counter-opening sides 5 b and 5 b. Therefore, the structures of the inner ring 2, outer ring 3, rolling element 4, and crown-shaped retainer 5 are not limited to any specific ones but they can be structured arbitrarily, and thus the detailed description thereof is omitted here.

[0130] According to the present embodiment, between the outer rings 3 and 3 of the rolling bearings 1 and 1, there are interposed spacers 7 and a preload Fao is applied to the inner rings 2 and 2 from the retainer pocket opening sides 5 a and 5 a, so that the preload can be applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b (see FIG. 1). By the way, the method for applying the preload is not limited but can be changed. Also, the amount of the preload is not limited to any specific amount but can be set at an optimum amount according to cases.

[0131] In the bearings 1 respectively incorporating the crown-shaped retainers 5 therein, since the preload is applied not only to the inner ring end faces 2 b and 2 b situated on the retainer pocket opening sides 5 a and 5 a but also to the outer ring end faces 3 b and 3 b situated on the retainer pocket counter-opening sides 5 b and 5 b, it is possible to design a bearing apparatus which can provide reduced torque and enhanced rotation accuracy. Also, the dust-production problem, which is found in the above-mentioned related bearing apparatus, can be solved by using a magnetic fluid seal. That is, as shown in FIG. 2, grease G, as the lubricant mentioned above, filled into the bearing raceways collects on the counter-contact-angle side and, especially due to the centrifugal force thereof, on the outer ring 3 side; and, grease G collecting on the counter-contact-angle side of the outer ring 3, with the rotation of the ball 4, is moved to the retainer pawl 5 e side in parallel to the contact angle (the moving direction is shown by an arrow mark A in FIG. 2), and the grease G is scraped in the vicinity of the retainer pawl 5 e. The thus scraped grease G accumulates between the pawls 5 e, which makes it possible to realize proper grease supply.

[0132] Also, the dust generation problem can be solved by using a magnetic fluid seal.

[0133] Second Embodiment

[0134] Now, FIG. 3 shows a second embodiment of a bearing apparatus according to the present invention.

[0135] The present embodiment is different from the first embodiment in that the pocket opening sides 5 a and 5 a of the retainers 5 and 5 of the two rolling bearings 1 and 1 are disposed opposed to each other and also in that a preload is applied not only to the end faces 2 c and 2 c of the inner rings 2 and 2 situated on the retainer pocket opening sides 5 a and 5 a but also to the end faces 3 c and 3 c of the outer rings 3 and 3 situated on the retainer pocket counter-opening sides 5 b and 5 b. Therefore, the inner rings 2, outer rings 3, rolling elements 4 and retainers 5 are not limited to any specific structures but can employ arbitrary structures and thus, by adopting the first embodiment, the detailed description thereof is omitted here.

[0136] According to the present embodiment, between the inner rings 2 and 2 of the rolling bearings 1 and 1, there are interposed spacers 7 and a preload Fao is applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b, so that the preload can be applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b (see FIG. 3). By the way, the method for applying the preload is not limited but can be changed. Also, the amount of the preload is not limited to any specific amount but can be set at an optimum amount according to cases.

[0137] In the present bearings 1 respectively incorporating the crown-shaped retainers 5 therein, since the preload is applied not only to the inner ring end faces 2 c and 2 c situated on the retainer pocket opening sides 5 a and 5 a but also to the outer ring end faces 3 c and 3 c situated on the retainer pocket counter-opening sides 5 b and 5 b, it is possible to design a bearing apparatus which can provide reduced torque and enhanced rotation accuracy. Also, the dust-production problem, which is found in the related bearing apparatus, can be solved by using a magnetic fluid seal.

[0138] By the way, in the first and second embodiments, the two bearings 1 and 1 are spaced from each other by the spacer 7. Alternatively, however, the two bearings 1 and 1 may also be spaced from each other by changing the widths of the inner and outer rings 2 and 3.

[0139] Third Embodiment

[0140] Now, FIG. 4 shows a third embodiment of a bearing apparatus according to the present invention.

[0141] The bearing apparatus according to the present embodiment comprises a housing 10 having a double row raceway 10 a and 10 a formed in the inner periphery thereof, a shaft 6 having a raceway 6 a so formed in one portion of the outer periphery thereof as to be opposed to one raceway 10 a of the housing 10, an inner ring 2 formed separately and fixable to the other portion of the outer periphery of the shaft 6 such that its raceway 2 a is opposed to the other raceway 10 a of the housing 10, and a plurality of rolling elements (balls) 4 . . . and 4 . . . incorporated into between one raceway 10 a of the housing 10 and the raceway 6 a of the shaft 6 as well as between the other raceway 10 a of the housing 10 and the raceway 2 a of the inner ring 2 through their respective crown-shaped retainers 5 and 5.

[0142] And, in the present embodiment, in FIG. 4, the left side of the shaft 6 is held and the right side end face 2 b of the right-side separately formed inner ring 2 is pushed to thereby apply a preload Fao. Therefore, this preload type provides a so called an O-type preload. The crown-shaped retainers 5 and 5 are incorporated in such a direction that their respective pocket counter-opening sides 5 b and 5 b are opposed to each other.

[0143] As described above, since the preload Fao is applied to the end face 2 b of the inner ring 2 while the crown-shaped retainers 5 and 5 of the two bearings are disposed in such a manner that the respective pocket counter-opening sides 5 b and 5 b are opposed to each other (that is, the crown-shaped retainers 5 and 5 of the two bearings are disposed in an outwardly facing manner that the respective pockets 5 d are not opposed to each other), similarly to the previously described first and second embodiments, grease G collecting on the counter-contact-angle side of the groove 10 a of the housing 10 is involved with the rotational movement of the ball 4 and is thereby moved in the rotation (about its own axis) rotation of the ball 4, this grease G is scraped by the crown-shaped retainers 5, and the thus scraped grease G collects between the pawls 5 e of the crown-shaped retainers 5 and is stabilized there (see FIG. 5). And, the detailed structures and operation effects of the inner rings 2, rolling elements 4, and crown-shaped retainer 5 are similar to those of the previously described first embodiment and thus the description thereof is omitted here.

[0144] Fourth Embodiment

[0145] Now, FIG. 6 shows a fourth embodiment of a bearing apparatus according to the present invention.

[0146] The present embodiment provides a similar structure to the previously described third embodiment but is different therefrom in that the shaft 6 has a stepped portion.

[0147] The remaining structures and a method for applying the preload as well as the operation effects of the present embodiment are the same as the third embodiment.

[0148] Fifth Embodiment

[0149] Now, FIG. 7 shows a fifth embodiment of a bearing apparatus according to the present invention.

[0150] According to the present embodiment, there is provided a bearing apparatus which comprises: a stepped housing 10 having a raceway 10 a formed in one portion of the inner periphery thereof; a stepped shaft 6 having a raceway 6 a so formed in one portion of the outer periphery thereof as to be opposed to the raceway 10 a formed in one portion of the inner periphery of the stepped housing 10; a plurality of rolling elements (balls) 4 incorporated into between the raceway 10 a of the housing 10 and the raceway 6 a of the shaft 6 through a crown-shaped retainer 5; and, a single ball bearing 1 in which an outer ring 3 is fixed to the stepped portion of the housing 10, an inner ring 2 is fixed to the shaft 6, and a plurality of rolling elements 4 . . . are incorporated into between the outer and inner rings 3 and 2 through a crown-shaped retainer 5.

[0151] The detailed structures of the respective composing parts of the fifth embodiment such as the inner ring 2, outer ring 3, rolling elements 4, and crown-shaped retainers 5, the preload applying method of the fifth embodiment, and the operation effects of the fifth embodiment are the same as the previously described third embodiment.

[0152] Sixth Embodiment

[0153] Now, FIG. 8 shows a sixth embodiment of a bearing apparatus according to the present invention.

[0154] A bearing apparatus according to the present embodiment comprises: a shaft 6 having a double row raceway 6 a, 6 a formed in the outer periphery thereof; a housing 10 having a raceway 10 a so formed in one portion of the outer periphery thereof as to be opposed to one raceway 6 a of the shaft 6; an outer ring 3 separately formed and fixable to the outer periphery of the housing 10 opposed to the other raceway 6 a of the shaft 6 in such a manner that its two raceways 3 a are opposed to each other; and, a plurality of rolling elements (balls) 4 . . . , 4 . . . incorporated into between the raceway 10 a of the housing 10 and one raceway 6 a of the shaft 6 as well as between the other raceway 6 a of the shaft 6 and the raceways 3 a of the outer ring 3 through the crown-shaped retainers 5 and 5.

[0155] And, in the present embodiment, in FIG. 8, the left side of the housing 10 is held and the separately formed outer ring 3 on the right side is pushed, whereby a preload Fao is applied. Therefore, the present preload provides a so called X-type preload. The crown-shaped retainers 5 and 5 are incorporated in a direction where the pocket opening sides 5 a and 5 a are opposed to each other.

[0156] The detailed structures of the respective composing parts of the sixth embodiment such as the outer rings 3, rolling elements 4, and crown-shaped retainers 5, and the operation effects of the sixth embodiment are the same as the previously described third embodiment.

[0157] Seventh Embodiment

[0158] Now, FIG. 9 shows a seventh embodiment of a bearing apparatus according to the present invention.

[0159] The present embodiment provides a similar structure to the previously described sixth embodiment but is different therefrom in that the housing 10 has a stepped portion.

[0160] The remaining structures and a method for applying the preload as well as the operation effects of the present embodiment are the same as the sixth embodiment.

[0161] Eighth Embodiment

[0162] Now, FIG. 10 shows an eighth embodiment of a bearing apparatus according to the present invention.

[0163] According to the present embodiment, there is provided a bearing apparatus which comprises: a stepped housing 10 having a raceway 10 a formed in one portion of the inner periphery thereof; a stepped shaft 6 having a raceway 6 a so formed in one portion of the outer periphery thereof as to be opposed to the raceway 10 a; and, a plurality of rolling elements (balls) 4 . . . incorporated into between the raceway 10 a of the housing 10 and the raceway 6 a of the shaft 6 through a crown-shaped retainer 5; and, a single ball bearing 1 in which an outer ring 3 is fixed to the stepped portion of the housing 10, an inner ring 2 is fixed to the shaft 6, and a plurality of rolling elements 4 . . . are incorporated into between the outer and inner rings 3 and 2 through a crown-shaped retainer 5. The present embodiment is substantially similar in structure to the previously described fifth embodiment. However, in the present embodiment, the crown-shaped retainers 5 and 5 are disposed in such a manner that their respective pocket opening sides 5 a and 5 a are opposed to each other; and, a so-called X-type preload is applied (the preload applying method of the present embodiment is the same as the sixth embodiment). Therefore, the operation effects of the present embodiment are the same as the sixth embodiment.

[0164] Ninth Embodiment

[0165] Now, FIG. 11 shows a ninth embodiment of a bearing apparatus according to the present invention.

[0166] According to the present embodiment, a bearing apparatus comprises: a housing 10 having a double row raceway 10 a and 10 a formed in the inner periphery thereof; a straight-shaped shaft 6; two inner rings 2 and 2 separately formed and fixed to the outer periphery of the shaft 6 in such a manner that their respective raceways 2 a and 2 a are opposed to the raceways 10 a and 10 a of the housing 10; and, a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the raceways 10 a, 10 a of the housing 10 and the raceways 2 a, 2 a of the inner rings 2, 2 through their respective crown-shaped retainers 5 and 5.

[0167] And, according to the present embodiment, one inner ring 2 is held and the other inner ring 2 is pushed, whereby a preload is applied. Therefore, this preload type provides a so called o type. The crown-shaped retainers 5 and 5 are incorporated in such a manner that their respective pocket counter-opening sides 5 b and 5 b are opposed to each other. The detailed structures of the respective composing parts of the ninth embodiment such as the inner rings 3, rolling elements 4, and crown-shaped retainers 5, and the operation effects of the ninth embodiment are the same as the previously described third embodiment.

[0168] Tenth Embodiment

[0169] Now, FIG. 12 shows a tenth embodiment of a bearing apparatus according to the present invention.

[0170] According to the present embodiment, a bearing apparatus comprises: a shaft having a double row raceway 6 a and 6 a formed in the outer periphery thereof; a straight-shaped housing 10; two outer rings 3 and 3 separately formed and fixed to the outer periphery of the housing 10 in such a manner that their respective raceways 3 a and 3 a are opposed to the raceways 6 a and 6 a of the shaft 6; and, a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the raceways 6 a, 6 a of the shaft 6 and the raceways 3 a, 3 a of the outer rings 3, 3 through their respective crown-shaped retainers 5 and 5.

[0171] And, according to the present embodiment, one outer ring 3 is held and the other outer ring 3 is pushed, whereby a preload is applied. Therefore, this preload type provides a so called X type. The crown-shaped retainers 5 and 5 are incorporated in such a direction that their respective pocket opening sides 5 b and 5 b are opposed to each other. The detailed structures of the respective composing parts of the tenth embodiment such as the inner rings 3, rolling elements 4, and crown-shaped retainers 5, as well as the operation effects of the tenth embodiment are the same as the previously described sixth embodiment.

[0172] By the way, additional description will be given below of the preload applying methods according to the embodiments shown in FIGS. 4 to 12. In the case of the separately formed portions, that is, between the shaft 6 and inner ring 2 as well as between the outer ring 3 and housing 10, the following two method can be applied between the shaft 6 and the inside diameter of the inner ring 2 as well as between the housing 10 and the outside diameter of the inner ring 3.

[0173] (1) A dead weight is put on them with a clearance between them and a given preload is applied to them; and, in this state, they are adhered and fixed to each other.

[0174] (2) They are pressure inserted with interference between them, and the rigidity of them is controlled using their torque or resonance frequencies; and then, a given preload is applied to them.

[0175] Eleventh Embodiment

[0176] Now, FIG. 13 shows an eleventh embodiment of a bearing apparatus according to the present invention.

[0177] According to the present embodiment, a bearing apparatus comprises: a shaft 6 having a double row raceway 6 a and 6 a formed in the outer periphery thereof; two outer rings 3, 3; a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the raceways 6 a, 6 a of the shaft 6 and the raceways 3 a, 3 a of the outer rings 3, 3 through their respective crown-shaped retainers 5 and 5; and, a spring 12 interposed between the two outer rings 3 and 3. In the present embodiment, a preload is applied to the two outer rings 3 and 3 by the spring 12 in a direction where the two outer rings 3 and 3 are moved away from each other (a so called O-type preload is formed); and, the retainers 5 and 5 are incorporated in a direction where their respective pocket counter-opening sides 5 b and 5 b are opposed to each other. In FIG. 13, reference character 9 designates a seal plate and 13 stands for a spring seat.

[0178] According to the present embodiment, in a state where the pocket counter-opening sides 5 b and 5 b of the crown-shaped retainers 5 and 5 of the two bearings are opposed to each other (that is, in an outwardly facing state where the retainer pockets 5 d and 5 d are not opposed to each other), the preload (O-type preload) is applied to the end faces 3 b and 3 b of the outer rings 3 and 3. Therefore, as shown in FIGS. 14A and 14B, grease G collecting on the counter-contact-angle sides of the outer rings 3 is involved with the rotational movement of the ball 4 and is thereby moved in the rotation (about its own axis) direction of the ball 4, the present grease G is scraped by the retainers 5, and the thus scraped grease G collects between the pawls 5 e and 5 e of the retainers 5 and becomes stable there.

[0179] By the way, FIG. 15 shows an example of a method for assembling the two bearings each including a shaft according to the present invention. The bearing to be incorporated first can be incorporated easily regardless of the direction of the retainer 5. To assemble the remaining bearing, with the spring 12 held through a spring retainer 14, the retainer 5 is previously inserted between the spring 13 and the outer ring 3 to be assembled. In FIG. 15, reference character 15 designates a retainer receiver and 16 stands for a crescent-shaped ball receiver. Next, the balls 4 are inserted into between the outer raceway 3 a and shaft raceway 6 a which are disposed eccentric to each other, the outer ring 3 is then made concentric with the shaft 6, after then, the balls 4 are disposed at regular intervals, the position of the retainer pocket 5 d is matched to the position of the balls 4, and the retainer 5 is then pushed into the bearing to thereby assemble the bearing. After then, the spring retainer 14 is removed and the spring 12 held by the spring retainer 14 is expanded and pressed against the outer ring 3 to thereby apply a preload to the outer ring.

[0180] Twelfth Embodiment

[0181] Now, FIG. 16 shows a twelfth embodiment of a bearing apparatus according to the present invention.

[0182] According to the present embodiment, two ball bearings 1 and 1 are inserted into a shaft 6 and, by pressure insertion or by adhesion, the two bearings are fixed to the shaft 6; and, a preload is applied to the outer rings 3 and 3 of the two bearings 1 and 1 by a spring 12 interposed between the two outer rings 3 and 3 in a direction where the two races 3 and 3 part away from each other. This preload is a so called O-type preload, and the crown-shaped retainers 5 and 5 of the two bearings 1 and 1 are disposed in such a manner that their respective pocket counter-opening sides 5 b and 5 b are opposed to each other (that is, in an outwardly facing direction where the pockets 5 d and 5 d of the retainers 5 are not opposed to each other). Thanks to this, the present embodiment has similar operation effects to the eleventh embodiment. Also, in the present embodiment, two seal plates 9 serve also as spring seats to thereby reduce the cost and size of the bearing apparatus. However, it is also possible to provide spring seats separately. By the way, each of the bearings 1 is a ball bearing which comprises an inner ring 2, an outer ring 3, rolling elements 4, a crown-shaped retainer 5, and a seal plate 9; that is, the bearing 1 is not limited to a specific structure.

[0183] Thirteenth Embodiment

[0184] Now, FIG. 17 shows a thirteenth embodiment of a bearing apparatus according to the present invention.

[0185] The present embodiment is different from the twelfth embodiment in that two bearings 1 and 1 differing in size are fixed to a shaft 6 by pressure insertion or by adhesion, and a preload is applied to the outer rings 3 and 3 of the bearings 1 and 1 by a spring 12 through their respective spring seats 13 in a direction where the outer rings 3 and 3 part away from each other. The remaining structures and operation effects of the present embodiment are similar to the twelfth embodiment.

[0186] Fourteenth Embodiment

[0187] Now, FIG. 18 shows a fourteenth embodiment of a bearing apparatus according to the present invention.

[0188] The present embodiment is different from the thirteenth embodiment in that the two seal plates 9 function also as spring seats. In this case, it is not necessary to provide the spring seats separately, which makes it possible to reduce the cost of the bearing apparatus. The remaining structures and operation effects of the present embodiment are similar to the thirteenth embodiment.

[0189] Fifteenth Embodiment

[0190] Now, FIG. 19 shows a fifteenth embodiment of a bearing apparatus according to the present invention. According to the present embodiment, a bearing apparatus comprises: a shaft 6 having a double row raceway 6 a, 6 a formed in the outer periphery thereof; a housing 10 having a stepped portion; two outer rings 3 and 3 separately formed and fixed to the inner periphery of the housing 10; and, a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the raceways 3 a, 3 a of the two outer rings 3, 3 and the raceways 6 a, 6 a of the shaft 6 through their respective crown-shaped retainers 5 and 5. And, while applying an X-type preload to the outer rings 3 and 3, which have been inserted with light pressure, in a direction where they approach each other, the outer rings 3 and 3 are adhered and fixed to the housing 10. The double-row crown-shaped retainers 5 and 5 are disposed in such a manner that their respective pocket opening sides 5 a and 5 a are opposed to each other.

[0191] As described above, since, in a state where the pocket opening sides 5 a and 5 a of the crown-shaped retainers 5 and 5 of the two bearings are opposed to each other, the X-type preload is applied to the outer rings 3 and 3 in the direction where they approach each other, grease collecting on the counter-contact-angle side of the outer rings 3 is involved with the rotational movement of the ball and is moved in the rotation (about its own axis) direction of the ball, this grease is scraped by the crown-shaped retainers 5, and the thus scraped grease collects and becomes stable between the pawls 5 e and 5 e of the retainers 5.

[0192] Sixteenth Embodiment

[0193] Now, FIG. 20 shows a sixteenth embodiment of a bearing apparatus according to the present invention. According to the present embodiment, there is provided a bearing apparatus which comprises: a housing 10 having a stepped portion; a shaft 6 having a raceway 6 a formed in one portion of the outer periphery thereof; an outer ring 3 separately formed and fixed to one portion of the inner periphery of the housing 10 such that it is opposed to the raceway 6 a; a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the raceway 3 a of the outer ring3 and the raceway 6 a of the shaft 6 through a crown-shaped retainer 5; and, a ball bearing 1 including an inner ring 2, an outer ring 3, a plurality of rolling elements 4, a crown-shaped retainer 5 and two seal plates 9. In this embodiment, while applying an X-type preload to the outer rings 3 and3 in a direction where they approach each other, the outer rings 3 and 3 are adhered and fixed to the housing 10. The inner ring 2 may be fixed by pressure insertion or by adhesion. The double-row crown-shaped retainers 5 and 5 are disposed in an inwardly facing direction where their respective pocket opening sides 5 a and 5 a are opposed to each other. In the present embodiment, there disposed another two seal plates (shield plates) 9 so as to extend between the separately formed outer ring 3 and the outer periphery of the shaft 6. The operation effects of the present embodiment are the same as the fifteenth embodiment.

[0194] Seventeenth Embodiment

[0195] Now, FIG. 21 shows a seventeenth embodiment of a bearing apparatus according to the present invention. According to the present embodiment, there is provided a bearing apparatus, which comprises: a shaft 6 having a raceway 6 a formed in one portion of the outer periphery thereof; an outer ring 3 so disposed as to be opposed to the raceway 6 a; a plurality of rolling elements 4 . . . to be incorporated into between the raceway 3 a of the outer ring 3 and the raceway 6 a of the shaft 6 through a crown-shaped retainer 5; a ball bearing 1 including an inner ring, an outer ring 3, a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the outer ring 3 and inner ring 2 through a crown-shaped retainer 5, the inner ring 2 being fixed to the shaft 6; and, a spring 12 interposed between the two outer rings 3 and 3. In this structure, a preload is applied to the two outer rings 3 and 3 by the spring 12 in a direction where the two outer rings 3 and 3 are moved away from each other. The inner ring can be fixed by pressure insertion or by adhesion. The two crown-shaped retainers 5 and 5 are disposed in such a direction that their respective pocket counter-opening sides 5 b and 5 b are opposed to each other. The remaining structures and operation effects of the present embodiment are the same as those of the previously described eleventh embodiment.

[0196] Eighteenth Embodiment

[0197] Now, FIG. 22 shows an eighteenth embodiment of a bearing apparatus according to the present invention. According to the present embodiment, there is provided a bearing apparatus, which comprises: a shaft 6; a housing 10; two inner rings 2 and 2; two outer rings 3 and 3; a plurality of rolling elements 4 . . . , 4 . . . to be incorporated into between the inner raceways 2 a, 2 a of the inner rings 2, 2 and the outer ringways 3 a, 3 a of the outer rings 3, 3 through their respective crown-shaped retainers 5 and 5; and, a spring 12 interposed between the two inner rings 2 and 2. In the present embodiment, a preload is applied by the spring 12 in a direction where the inner rings 2 and 2 are moved away from each other (that is, the present preload provides a so called X-type preload); and, the two retainers 5 and 5 are incorporated in such a direction that their respective pocket opening sides 5 a and 5 a are opposed to each other. The remaining operation effects of the present embodiment are the same as those of the second embodiment.

[0198] Nineteenth Embodiment

[0199] Now, FIG. 23 shows a nineteenth embodiment of a bearing apparatus according to the present invention. According to the present embodiment, there is provided a bearing apparatus, which comprises: a housing 10 having a double row raceway 10 a and 10 a formed in the inner periphery thereof; a shaft 6 having a raceway 6 a opposed to one raceway 10 a of the housing 10 and also including a stepped portion 6 b; an inner ring 2 formed separately and fixed to the outer periphery of the shaft 6 in such a manner that its raceway 2 a is opposed to the other raceway 10 a of the housing 10; a plurality of rolling elements 4 4 . . . to be incorporated into between one raceway 10 a of the housing 10 and the raceway 6 a of the shaft 6 as well as between the other raceway 10 a of the housing 10 and the inner raceway 2 a of the inner ring 2 through their respective crown-shaped retainers 5 and 5; and, a spring 12 interposed between the separately formed inner ring 2 and the stepped portion 6 b of the shaft 6. In the present embodiment, a preload is applied by the spring 12 in a direction where the separately formed inner ring 2 and the stepped portion 6 b of the shaft 6 are moved away from each other (that is, the present preload provides a so called X-type preload); and, the two retainers 5 and 5 are incorporated in such a direction that their respective pocket opening sides 5 a and 5 a are opposed to each other. The remaining operation effects of the present embodiment are the same as those of the second embodiment.

[0200] Twentieth Embodiment

[0201] To be able to apply the preload Fao from the inner ring 2 on the retainer opening side 5 a or from the outer ring 3 on the retainer counter-opening side 5 b, when assembling the bearing 1 to the shaft 6, the incorporating direction of the crown-shaped retainer 5 must be known. Especially, in the case of the bearing 1 incorporating the two seal plates 9 therein, it is difficult to distinguish the incorporating direction of the crown-shaped retainer 5 from the outside.

[0202] In view of the above, as shown in FIGS. 24A and 24B, preferably, between one end face 1 a and the other end face 1 b of the bearing 1 in the axial direction thereof (in FIG. 24A, in the right and left direction), there may be provided arrangements (distinctive arrangements) which allow the incorporating direction of the crown-shaped retainer 5 to be distinguished easily from the outside.

[0203] As the distinctive arrangements to be provided between the two end faces 1 a and 1 b, there can be employed the following arrangements. Such retainer incorporating direction distinctive arrangements can be properly selected in all of the above-mentioned first to nineteenth embodiments or in other arbitrary embodiments.

[0204] Now, description will be given below of the retainer incorporating direction distinctive arrangements as well as the operation effects thereof.

[0205] For example, as shown in FIG. 24B, marks 11 and 11, which indicate the retainer incorporating direction, may be provided on only one end face 2 b and/or 3 b of one or both of the inner and outer rings 2 and 3. These marks 11, 11, as shown in FIG. 24B, may be applied to the inner ring end face 2 b and outer ring end face 3 b of the bearing situated on the retainer opening side 5 a. In case where the marks 11, 11 are applied to the inner ring end face 2 b and outer ring end face 3 b of the bearing situated on the retainer opening side 5 a in this manner, the end face with the marks 11, 11 applied thereto provides the retainer opening side 5 a, which makes it possible to distinguish the retainer incorporating direction simply and instantaneously.

[0206] By the way, the marks 11, reversely to the illustrated example, may also be applied to the inner ring end face 2 c and outer ring end face 3 c of the bearing situated on the retainer counter-opening side 5 b. In this case, the marks 11 indicate the incorporation start position side of the retainer 5 and, naturally, it can be confirmed that the end face side with no marks thereon is the opening side 5 a.

[0207] As the mark 11, in FIG. 24, an x mark is used but this is just an example and the mark can be selected arbitrarily. As the mark 11, a separately formed mark may be bonded, or a mark may be engraved directly in the end face, or a plane-shaped or projection-shaped mark may be provided; and, the number of marks and the positions thereof may also be selected arbitrarily. Also, the mark 11 can be provided only one of the end faces 2 b and 3 b.

[0208] Further, the mark 11 may also be applied to the seal plate 9 which is opposed to either of the retainer pocket opening side 5 a or the retainer pocket counter-opening side 5 b. In this case, similarly to the above-mentioned arrangements, the retainer incorporating direction can be distinguished instantaneously.

[0209] Also, in case where the sealplates 9 and 9 are made different in color and material from each other to thereby cause the seal plate 9 on one end side of the bearing to differ in structure from the seal plate 9 on the other end side of the bearing, the incorporating direction of the retainer 5 can also be distinguished from the outside. For example, in case where the color and patterns of both of the seal plates 9 and 9 are made different from each other, or in case where one of the seal plates 9 is made of synthetic resin or rubber and the other seal plate 9 is made of steel material, the incorporating direction of the retainer 5 can also be distinguished from the outside.

[0210] Further, when the seal plate is made of synthetic resin, in case where transparent synthetic resin is used, the incorporating direction of the retainer 5 can be confirmed through the transparent seal plate And, as illustrated in the seventeenth embodiment (FIG. 21), by making different the shapes and sizes of the two seal plates from each other, the incorporating direction of the retainer 5 can be distinguished.

[0211] Also, when the ball bearing 1 is assembled to such shaft 6 as shown FIGS. 16, 17 and 18, in case where, instead of mounting the seal plates 9 on the two end portions of the bearing 1 as in the above-described embodiments, they are mounted on only one of the bearing end faces, the incorporating direction of the retainer 5 can be distinguished from the outside. That is, in case where the seal plate 9 is mounted only on the bearing end face situated on the counter-opening side 5 b of the crown-shaped retainer 5 or only on the bearing end face situated on the opening side 5 a of the crown-shaped retainer 5, the seal plate 9 mounting side provides the retainer opening side 5 a (or retainer counter-opening side 5 b), so that the incorporating direction of the retainer 5 can be distinguished easily.

[0212] Further, in case where undulations such as notches are formed in the axial-direction end edge portions of one or both of the inner and outer rings 2 and3 to thereby provide a distinctive arrangement, the incorporating direction of the retainer can be distinguished. According to this distinctive arrangement, an automatic machine for assembling an HDD can be structured such that, while distinguishing the incorporating direction of the retainer 5 through the undulations such as notches, it is able to assemble the bearing to the shaft in a given direction.

[0213] In the process for manufacturing a bearing with a seal, an operation to provide a distinctive arrangement between the two end faces of the bearing according to the retainer incorporating direction can be carried out easily and positively without incurring any troublesome operation.

[0214] In the case of the above-structured two ball bearings each having a seal, since the retainer incorporating direction can be distinguished easily and positively from the outside, the assembling directions of the respective bearings can be controlled positively according to their respective retainer incorporating directions.

[0215] In case where the above-mentioned rolling bearing 1 structure is employed, since there can be provided various distinctive arrangements which allow the incorporating direction of the crown-shaped retainer 5 to be distinguished from the outside, for example, even in the case of the bearing with the seal plates 9 and 9 mounted on the two end portions thereof, the incorporating direction of the crown-shaped retainer 5 can be distinguished easily from the outside.

[0216] Thanks to this, since the preload Fao can be applied easily and positively to the portion of the inner ring 2 on the retainer opening side 5, the rotation torque of the bearing apparatus and variations in such rotation torque as well as the vibrations of the bearing apparatus not synchronous with the rotation thereof can be reduced.

[0217] Description of Tests

[0218] Here, description will be given below of tests conducted in order to confirm the effects of the bearing apparatus described hereinbefore.

[0219] Firstly, the movement of the grease existing in the interior portion of the bearing was observed. FIGS. 27A and 27B are schematic views of observation test apparatuses. In the present test, in order to be able to confirm the movement of the grease, the counter-load side portion 3′ of the outer ring 3 of the bearing and the seal plate 9 portion are made of transparent acrylic acid resin. In observation, an electric flash S or a high-speed video V was used and the movement of the grease was photographed while rotating the inner ring 2.

[0220] The grease was colored with a dye and was filled into the space of the retainer 5 on the pocket counter-opening side 5 b.

[0221]FIG. 27A shows a structure where a preload Fao is applied to the inner ring end face on the retainer counter-opening side 5 b and to the outer ring end face on the retainer opening side 5 a ((1) which is also referred to as a structure according to the prior art); and, FIG. 27B shows a structure where a preload is applied to the inner ring end face on the retainer opening side 5 a and to the outer ring end face on the retainer counter-opening side 5 b ((2) which is also referred to as a structure according to the present invention).

[0222] (1) In the Case of the Structure According to the Prior ArtH

[0223] Grease existing on the raceway surface 3 a of the outer ring 3, due to passage of the ball 4, is discharged out of the raceway surface 3 a, and most of the grease flows to the pocket counter-opening side 5 b of the retainer 5 (that is, the outer ring counter-load side direction) and joins grease which flows in the radial direction from between the pocket counter-opening side 5 b end face and seal 9 inner surface.

[0224] On the other hand, a little grease collecting in a space on the retainer pocket opening side 5 a, only when it touches the ball 4, is allowed to flow through the ball 4, whereas the other remaining grease little flows.

[0225] (2) In the Case of the Structure According to the Present Invention

[0226] Grease existing on the raceway surface 3 a of the outer ring 3, due to the passage of the ball 4, is discharged out of the raceway surface 3 a, and most of the grease flows to the pocket opening side 5 a of the retainer 5 (that is, the outer ring counter-load side direction) and collects in a space on the retainer pocket opening side 5 a. The grease, only when it touches the ball 4, is allowed to flow and the other remaining grease little flows.

[0227] On the other hand, a little grease flowing to the retainer pocket counter-opening side 5 b joins grease which flows outwardly in the radial direction from between the pocket counter-opening side 5 b end face and seal 9 inner surface.

[0228] The above test results show that, in both of the (1) and (2) structures, in the case of the grease existing on the outer raceway surface 3 a (the grease, which touches the ball 4, inner ring 2 and retainer 5 and receives a centrifugal force, is splashed outwardly in the radial direction and is easy to be supplied to the outer ring side), due to the passage of the ball 4 through the raceway surface 3 a, most of the grease flows in the outer ring counter-load side direction. Therefore, in the case of the (1) structure, the grease is easy to touch the retainer 5 and thus the fluidity of the grease is active. On the other hand, in the case of the (2) structure, the grease is easy to collect in the space on the retainer pocket opening side 5 a and thus, when compared with the (1) structure, the fluidity of the grease is low.

[0229] First Test

[0230] Next, FIG. 28 shows the results of a test conducted in order to confirm the effects of the present embodiment. In the test, there were used a bearing apparatus (FIG. 44) according to the prior art employing the preload pattern of the (1) structure and a bearing apparatus (FIG. 1) according to the present invention employing the preload pattern of the (2) structure, and an increase in the bearing temperature (a value obtained by subtracting the atmospheric temperature from the outer ring temperature) was measured. The test conditions were the same in both of them except that, as described above, the preload patterns were different.

[0231] Bearing: Single-row deep-raceway ball bearing having an inside diameter 30 mm, an outside diameter 72 mm and a width 19 mm

[0232] Number of rotations: 50s⁻¹ (3000 rpm) (inner ring rotation)

[0233] Preload: Axial load 490N

[0234] Test time: 5 hours

[0235] As can be seen from FIG. 28, when compared with the prior art (the related bearing apparatus), the present invention (the bearing apparatus according to the present embodiment) is low in an increase in the temperature and is also low in torque. Therefore, with use of the present invention, the flow of the grease in the interior portion of the bearing settles in an early stage and thus a reduction in the torque of the bearing can be realized.

[0236] By the way, although the present test was conducted using an inner ring rotation system, in the case of an outer ring rotation system as well, it can be expected that the fluidity of the grease existing on the outer raceway is similar to the inner ring rotation system; and, therefore, in both of the inner ring and outer ring rotation systems, with use of the preload pattern employed in the present invention, a reduction in the torque can be attained.

[0237] Also, in case where an axial load and a radial load are applied at the same time, the contact angle does not provide an angle of 0° and thus the effects of this case may be considered to be similar to the above-mentioned embodiment of the present invention.

[0238] Second Test

[0239] Next, in a second test, the bearing apparatus having the related structure (FIG. 44) and the bearing apparatus having the structure according to the present invention (FIG. 1) were disposed on the HDD/SPM apparatus shown in FIG. 29, and time series variations in the torque and NRRO of the two bearing apparatus were compared.

[0240] By the way, in the present test, the end face 2 b of the inner ring 2 in one bearing (in FIG. 29, the lower bearing) was butted against a stepped portion 6 a raised formed on one end side of the shaft 6 of the HDD/SPM apparatus; between the outer rings 3 and 3 of the two bearings 1 and 1, there were interposed the stepped portions 8 that are formed in the inside diameter surface of the housing; and, a weight or a spring force equal to a desired preload was applied to the end face 2 b of the inner ring 2 of the other bearing (in FIG. 29, the upper bearing) to thereby fix the inner ring 2 to the shaft 6 by adhesion. In this case, instead of adhesion, the inner ring 2 may also be fixed by pressure insertion.

[0241] Bearing: Miniature ball bearing for information equipment, having an inside diameter 5 mm, an outside diameter 13 mm, a width 3 mm

[0242] Numberof rotations: 120s⁻¹ (7200 rpm) (outer ring rotation)

[0243] Preload: Axial load 11.76N (1.2 kgf)

[0244] Test time: 2 Hrs.

[0245]FIGS. 29 and 30 show the results of the comparison second test. Specifically, FIG. 30 shows the results of the structure according to the present invention, whereas FIG. 29 shows the results of the related structure (in the respective figures, FIGS. 29A and 30A show the time series variations in the torque and FIGS. 29B and 30B show the time series variations in NRRO). These results show clearly that the bearing apparatus according to the present invention is small in the torque and variations in the torque as well as in NRRO. When these results are compared with the results of the related bearing apparatus, it can be confirmed that the bearing apparatus according to the present invention is better in both torque and NRRO than the related bearing apparatus. By the way, in the present test example, there was employed the outer ring rotation system but, in the case of the inner ring rotation system as well, a similar effect could be actually confirmed. Also, the number of rotations and the quantity of the preload are not limited to any specific values.

[0246] Now, description will be given below of the preferred embodiments of the present invention with reference to the accompanying drawings. By the way, these embodiments are simply examples of the mode for carrying out the present invention and thus the present invention is not limited to these embodiments at all.

[0247]FIGS. 24A and 24B show embodiments of a rolling bearing according to the present invention. FIGS. 25 and 26 respectively show twenty-first and twenty-second embodiments of a bearing apparatus according to the present invention, in which the rolling bearing shown in FIGS. 24A and 24B is fixed to a shaft.

[0248] A rolling bearing 1 comprises an inner ring 2 having an inner raceway 2 a formed in the outer peripheral surface thereof, an outer ring 3 having an outer raceway 3 a formed in the inner peripheral surface thereof, a plurality of rolling elements 4 rotatably interposed between the inner raceway 2 a and outer raceway 3 a, and a crown-shaped retainer 5 for holding the rolling elements 4 at regular intervals; and, between the outer peripheral surfaces of the axial-direction two end portions of the inner ring 2 and the inner peripheral surfaces of the two end portions of the outer ring 3, there are interposed a pair of seal rings (in the present embodiment, shields) 9 and 9 each formed as a circular ring shape to thereby close spaces between these inner ring and outer ring peripheral surfaces.

[0249] And, into a space 8 defined by the pair of seal rings 9, there is filled grease from the one-end opening side of the space 8. By the way, the seal ring 9 is not limited to a specific structure but, due to the low torque thereof, preferably, it may have a non-contact-type seal (shield) structure. However, as the need arises, a contact-type seal can also be mounted. Also, in the present embodiment, the two seal rings 9 and 9 are respectively mounted on the two end portions of the bearing; however, as the need arises, a seal ring 9 can also be mounted only on one end portion of the bearing.

[0250] Especially, the rolling bearing 1 according to the present invention is characterized in that, between one end face la and the other end face 1 b of the rolling bearing 1 in the axial direction (in FIG. 24A, the right and left direction) thereof, there is provided indicating arrangement capable of indicating the incorporating direction of the retainer 5. Therefore, in the following description, importance is placed on the characteristic portion of the present rolling bearing 1. That is, since the structures of the remaining portions such as the inner ring 2, outer ring 3, rolling elements 4, seal rings 9 and grease are not limited to the illustrated ones but there can be employed arbitrary structures, the detailed description thereof is omitted here.

[0251] As the typical means for distinguishing the two end faces 1 a and 1 b from each other in the above manner, for example, there can be employed the following structures.

[0252] That is, as shown in FIGS. 24A and 24B, marks 11 and 11 for indicating the incorporating direction of the retainer may be given only to one or both of the one-side end faces 2 c and 3 c of the inner and outer rings 2 and 3.

[0253] The marks 11 and 11, for example, as shown in FIG. 24B, may be given to the bearing inner ring end face 2 c and outer ring end face 3 c which are situated on the retainer opening side 5 a. In case where the marks 11 and 11 are given to the bearing inner ring end face 2 c and outer ring end face 3 c of the retainer opening side 5 a in this manner, the end face with the marks 11 and 11 given thereto shows the retainer opening side 5 a. By the way, the marks 11 may be disposed in reverse to the embodiment shown in FIGS. 24A and 24B; that is, they can also be attached to the bearing inner ring end face 2 b and outer ring end face 3 b which are situated on the counter-opening side 5 b of the retainer 5. In this case, the marks 11 show the incorporation start position side of the retainer 5, which naturally makes it possible to confirm that the end face side with the marks 11 not given thereto is the opening side 5 a. Although, in FIG. 24B, there is shown the mark x as an example of the mark 11, the mark 11 is not limited to the mark x but the kinds of the mark 11 can be selected arbitrarily. The mark 11 may be engraved or may be formed in a plane or in a projection shape; and, the number and position of the mark 11 can be selected arbitrarily. Also, the mark 11 may also be disposed in one of the seal rings 9.

[0254] Also, alternatively, the seal rings 9 and 9 separating the two sides of the space 8 may also be made of different material so that the colors of the seal rings 9 on the bearing one end side and the other end side can be made different from each other. In this case as well, the incorporating direction of the retainer 5 can be distinguished from the outside.

[0255] And, instead of mounting the seal rings 9 respectively on the two end portions of the bearing 1 in the above-mentioned manner, a seal ring 9 may also be mounted only one of the bearing end faces; and, in this case as well, the incorporating direction of the retainer 5 can be distinguished from the outside. That is, in case where the seal ring 9 is mounted only on the bearing end face situated on the counter-opening side 5 b of the retainer 5 or on the bearing end face situated on the opening side 5 a of the retainer, the seal ring 9 mounting side provides the retainer opening side 5 a (or the retainer counter-opening side 5 b), which can facilitate the distinction of the incorporating direction of the retainer 5.

[0256] Further, undulations (recesses and projections) such as notches may also be formed in the axial-direction end edge portion(s) of one or both of the above inner and outer rings 2 and 3 to thereby provide retainer incorporating direction indicating arrangement. In this case as well, the retainer incorporating direction can distinguished.

[0257] Thanks to the above-structured rolling bearing, an automatic assembling machine for assembling an HDD can also be structured such that, while distinguishing the incorporating direction of the retainer 5 from the undulations such as the notches, the bearing can be assembled in a given direction.

[0258] In a process for manufacturing a rolling bearing with a seal, provision of indicating arrangement between the above-mentioned two end faces according to the retainer incorporating direction can be attained easily and positively without executing any specially troublesome operation.

[0259] In the case of the above-structured rolling bearing with a seal according to the present invention, since the retainer incorporating direction can be distinguished easily and positively from the outside, the assembling direction of the respective bearings can be positively controlled according to the retainer incorporating direction.

[0260] Also, in a bearing apparatus structured such that the rolling bearing 1 is fixed to the shaft 6, to reduce the rotation torque of the bearing apparatus and variations in such rotation torque as well as the vibrations of the bearing apparatus that are not synchronous with the rotation thereof (which is also referred to as NRRO), as shown in FIGS. 25 and 26, it is effective to apply a preload Fao to the inner ring 2 of the retainer opening side 5 a; and, for this purpose, when assembling the bearing 1 to the shaft, the incorporating direction of the retainer 5 must be known.

[0261] With employment of the above-mentioned bearing 1 structure, since, in the seal rings 9 or races (inner ring 2 and outer ring 3) of the bearing 1, there are provided various indicating arrangement by which the incorporating direction of the retainer 5 can be distinguished from the outside, for example, even in the case of a bearing with the seal rings 9 and 9 mounted on the two ends 1 a and 1 b thereof, the incorporating direction of the retainer 5 can be distinguished easily. Therefore, the preload Fao can be applied to the inner ring 2 on the retainer opening side 5 a easily and positively, which makes it possible to reduce the rotation torque of the bearing apparatus and variations in such rotation torque as well as the vibrations of the bearing apparatus that are not synchronous with the rotation thereof.

[0262] Now, FIG. 25 shows a twenty-first embodiment of a bearing apparatus according to the present invention, which comprises two bearings 1 and 1. Specifically, the inner rings 2 and 2 of the two bearings 1 and 1 are respectively fixed to the outer periphery of a shaft 6, the counter-opening sides 5 b and 5 b of the retainers 5 and 5 of the two bearings 1 and 1 are respectively opposed to each other and, between the outer rings 3 and 3 of the two bearings 1 and 1, there is interposed an spacer 7. In this structure, by applying a preload Fao to the inner rings 2 and 2 from the retainer opening sides 5 a and 5 a, the preload can be applied to the outer rings 3 and 3 from the retainer counter-opening sides 5 b.

[0263] According to the present embodiment, the two bearings 1 and 1 are combined together in such a manner that the marks 11 shown in FIGS. 24A and 24B are not opposed to each other: that is, in the case of the bearing 1 situated on the upper side in the axial direction of the bearing apparatus in FIG. 25, the marks 11 are provided on the one-side end faces (in FIG. 25, the upper end faces) 2 c and 3 c of the inner and outer rings 2 and 3; and, in the case of the lower-side bearing 1, the marks 11 are provided on the one-side end faces (in FIG. 25, the lower end faces) 2 c and 3 c of the inner and outer rings 2 and 3. By the way, a method for applying the preload is not limited to any specific one. Also, the quantity of the preload can be set at the optimum quantity according to cases. Further, the dust generation problem can be solved by using a magnetic fluid seal.

[0264] Now, FIG. 26 shows a twenty-second embodiment of a bearing apparatus according to the present invention, which comprises two bearings 1 and 1. Specifically, the inner rings 2 and 2 of the two bearings 1 and 1 are respectively fixed to the outer periphery of a shaft 6, the opening sides 5 a and 5 a of the retainers 5 and 5 of the two bearings 1 and 1 are opposed to each other, and there is interposed an spacer 7 between the two inner rings 2 and 2. In this structure, by applying a preload Fao to the outer rings 3 and 3 of the two bearings 1 and 1 from the retainer counter-opening sides 5 b and 5 b, the preload can be applied to the inner rings 2 and 2 from the retainer opening sides 5 a.

[0265] According to the present embodiment, the two bearings 1 and 1 are combined together in such a manner that the marks 11 shown in FIGS. 24A and 24B are opposed to each other: that is, in the case of the bearing 1 situated on the upper side in the axial direction of the bearing apparatus in FIG. 26, the marks 11 are provided on the one-side end faces (in FIG. 26, the lower end faces) 2 c and 3 c of the inner and outer rings 2 and 3; and, in the case of the lower-side bearing 1, the marks 11 are provided on the one-side end faces (in FIG. 26, the upper end faces) 2 c and 3 c of the inner and outer rings 2 and 3. By the way, a method for applying the preload, the quantity of the preload and the dust generation problem are similar to the twenty-first embodiment shown in FIG. 25.

[0266] By the way, in the illustrated embodiments, description has been given by employing a structure in which the two bearings 1 and 1 are used as a pair. However, the present invention is not limited to the combination of the two bearings.

[0267] Now, description will be given below of the preferred embodiments of a bearing apparatus according to the present invention with reference to the accompanying drawings. By the way, the present embodiments are just an example of the present invention and thus the present invention is not limited to them at all. Also, in the present embodiments, description will be given employing a structure in which two bearings are used as a pair. However, the present invention is not limited to such structure that two bearings are combined together as a pair.

[0268] Twenty-Third Embodiment

[0269] Now, FIG. 25 shows a twenty-third embodiment of a bearing apparatus according to the present invention. In the present bearing apparatus, two deep-groove rolling bearings 1 and 1 each using a crown-shaped retainer 5 shown in FIG. 32 are combined together as a pair in such a manner that the inner rings 2 and 2 of the respective rolling bearings 1 and 1 are fixed to the outer periphery of a shaft 6 and a preload is applied to the inner rings 2 and 2 on the pocket opening sides 5 a and 5 a of the retainers 5.

[0270] Especially, according to the present invention, in a bearing apparatus composed of a pair of bearings 1 and 1 with lubricants sealed into the raceway surfaces 2 a and 3 a of the inner and outer rings 2 and 3 thereof, torque can be reduced and rotation accuracy can be enhanced.

[0271] The rolling bearing 1 is composed of an inner ring 2 having an inner raceway surface 2 a formed on the outer periphery thereof, an outer ring 3 having an outer raceway surface 3 a formed on the inner periphery thereof, a plurality of rolling elements 4 to be incorporated into between the inner raceway surface 2 a and outer raceway surface 3 a, and a crown-shaped retainer 4 for holding the rolling elements uniformly. Also, between the inner and outer rings 2 and 3 of the two bearings 1, as the need arises, there may be interposed seal plates (in the present embodiment, shields) 9 respectively. The structure of the seal plate 9 is not limited to a specific one but can be changed without departing from the scope of the present invention.

[0272] Now, FIG. 32 shows an embodiment of a crown-shaped retainer 5 for a bearing which is used in a bearing apparatus according to the present invention. The retainer 5 is injection molded using a molding metal mold which is worked by shot blast or by electric discharge machining so as to provide such surface roughness having the maximum height Ry being of 3 to 50 μm or so. By the way, the basic shape of the retainer 5 can be selected arbitrarily. Therefore, on the surface of the retainer 5, there are innumerably and randomly formed delicate recessed portions 5 d, . . . which serve as lubricating oil standing portions. By the way, in the present embodiment, while the recessed portions 5 d are formed on the entire surface of the retainer 5, the surface roughness of at least the pocket surface (rolling element sliding contact surface) 5 c of the retainer 5 may only be formed such that it has the above-mentioned maximum height Ry. Due to lubricants held in the recessed portions, there are formed oil films between the rolling surfaces of the rolling elements 4 and the inner surface of the retainer pocket to thereby allow the rolling elements 4 to roll smoothly. Also, the lubricants stuck to the rolling surfaces of the rolling elements 4 are fed to the rolling contact portions of the rolling surfaces of the rolling element 4 with respect to the inner raceway surface and outer raceway surface, thereby being able to enhance the lubricating conditions of these rolling contact portions of the rolling elements 4.

[0273] As described above, the rolling bearing 1 is not limited to a specific structure but employs a general structure. The present embodiment is characterized in that: the crown-shaped retainer 5 with the surface roughness thereof adjusted is incorporated into the bearing 1; the retainers 5, 5 pocket counter-opening sides 5 b, 5 b of the two bearings 1, 1 are disposed opposed to each other; and, a preload is applied not only to the inner ring end faces 2 b, 2 b situated on the retainer pocket opening sides 5 a, 5 a but also to the outer ring end faces 3 b, 3 b situated on the retainer pocket counter-opening sides 5 b, 5 b. Therefore, the inner ring 2, outer ring 3, rolling elements 4 and retainer 5 are not limited to any specific structures but can employ arbitrary structures and thus the detailed description thereof is omitted here.

[0274] According to the present embodiment, between the outer rings 3 and 3 of the rolling bearings 1 and 1, there are interposed spacers 7 and a preload Fao is applied to the inner rings 2 and 2 from the retainer pocket opening sides 5 a and 5 a, so that the preload can be applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b (see FIG. 32). By the way, the method for applying the preload is not limited but can be changed. Also, the amount of the preload is not limited to any specific amount but can be set at an optimum amount according to cases.

[0275] In the bearings 1 respectively incorporating the crown-shaped retainers 5 therein, since the preload is applied not only to the inner ring end faces 2 b and 2 b situated on the retainer pocket opening sides 5 a and 5 a but also to the outer ring end faces 3 b and 3 b situated on the retainer pocket counter-opening sides 5 b and 5 b, it is possible to design a bearing apparatus which can provide reduced torque and enhanced rotation accuracy. Also, the dust-production problem, which is found in the above-mentioned related bearing apparatus, can be solved by using a magnetic fluid seal.

[0276] Twenty-Fourth Embodiment

[0277] Now, FIG. 26 shows a twenty-fourth embodiment of a bearing apparatus according to the present invention.

[0278] The present embodiment is different from the twenty-third embodiment in that the pocket opening sides 5 a and 5 a of the retainers 5 and 5 of the two rolling bearings 1 and 1 are disposed opposed to each other and also in that a preload is applied not only to the end faces 2 c and 2 c of the inner rings 2 and 2 situated on the retainer pocket opening sides 5 a and 5 a but also to the end faces 3 c and 3 c of the outer rings 3 and 3 situated on the retainer pocket counter-opening sides 5 b and 5 b. Therefore, the inner rings 2, outer rings 3, rolling elements 4 and retainers 5 are not limited to any specific structures but can employ arbitrary structures and thus, by adopting the twenty-third embodiment, the detailed description thereof is omitted here. In addition to this, the retainers 5, as same as the structure shown in the twenty-third embodiment, employs the crown-shaped retainer with rolling element sliding contact surface thereof formed as a rough surface.

[0279] According to the present embodiment, between the inner rings 2 and 2 of the rolling bearings 1 and 1, there are interposed spacers 7 and a preload Fao is applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b, so that the preload can be applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b (see FIG. 26). By the way, the method for applying the preload is not limited but can be changed. Also, the amount of the preload is not limited to any specific amount but can be set at an optimum amount according to cases.

[0280] In the present bearings 1 respectively incorporating the crown-shaped retainers 5 therein, since the preload is applied not only to the inner ring end faces 2 c and 2 c situated on the retainer pocket opening sides 5 a and 5 a but also to the outer ring end faces 3 c and 3 c situated on the retainer pocket counter-opening sides 5 b and 5 b, it is possible to design a bearing apparatus which can provide reduced torque and enhanced rotation accuracy. Also, the dust-production problem, which is found in the related bearing apparatus, can be solved by using a magnetic fluid seal.

[0281] Here, description will be given below of a third test conducted in order to confirm the effects of the present invention.

[0282] In the third test, the bearings were incorporated into an apparatus shown in FIG. 31 and variations in current values (which are converted to torque) with passage of time were measured.

[0283] By the way, in the present test, the end face 2 b of the inner ring 2 of one bearing (in FIG. 25, the lower bearing) was butted against a stepped portion 6 a raised formed on one end side of the shaft 6 of the apparatus, a stepped portion 8 formed in the periphery of the inside diameter surface of a housing is situated between the outer rings and 3 of the two bearings 1 and 1, and a weight or a spring force equal to a desired preload was applied to the end face 2 b of the inner ring 2 of the other bearing (in FIG. 25, the upper bearing) 1 to thereby adhere and fix to the shaft 6. In this case, instead of adhesion, the end face 2 b may also be pressure inserted into the shaft 6.

[0284] Bearing: Inside diameter 5 mm, outside diameter 13 mm, width 4 mm (corresponding to JIS 695)

[0285] Number of rotations: 7200 min⁻¹ (Outer ring rotation)

[0286] Preload: Axial load 11.8N

[0287] Measuring samples are shown in Table 1. TABLE 1 The Present Comparison Comparison Comparison Invention Example 1 Example 2 Example 3 Retainer -> Spherical Spherical Circular pocket shape surface, surface, cylinder Pocket surface Pocket surface Pocket surface roughness Ry = roughness Ry = roughness Ry = 10 μm 1 μm or less 1 μm or less Guide type Ball guide Ball guide Inner ring guide Preload direction Retainer Retainer pocket Retainer pocket Retainer pocket pocket counter-opening counter-opening counter-opening opening side inner ring side inner ring side inner ring side inner ring

[0288]FIG. 33 shows the results of the above third test. In FIG. 33, data shown by a solid line express the present invention, data shown by a chained line express the comparison example 1, data shown by a one-dot chained line express the comparison example 2, and data shown by a two-dot chained line express the comparison example 3, respectively.

[0289] As can be seen from the third test results, according to the structure of the present invention, even in case where a retainer with its pocket surface (sliding contact surface) roughness increased is used, the dynamic friction torque can be reduced and stabilized when compared with the related bearing.

[0290] By the way, in case where the retainer pocket surface roughness exceeds the maximum height Ry=50 μm, unfavorably, during the injection molding, burrs can be produced and dimension accuracy can be deteriorated: that is, high rotation accuracy is required. For example, the maximum height Ry for the HDD spindle motor or VCR may be preferably set for 10 μm or less. Also, in case where the maximum height Ry is less than 3 μm, the holding capacity of the lubricant is unfavorably short. This shows that, as described above, the maximum height Ry may be preferably set in the range of 3 to 50 μm.

[0291] Now, description will be given below of twenty-fifth and twenty-sixth embodiments of a bearing apparatus according to the present invention with reference to the accompanying drawings. By the way, the illustrated embodiments are just an example of the present invention and the present invention is not limited to them at all.

[0292]FIG. 25 shows a twenty-fifth embodiment of a bearing apparatus according to the present invention.

[0293] The present bearing apparatus comprises two rolling bearings 1 and 1. Specifically, the two rolling bearings 1 and 1 are combined together in the following manner: that is, the inner rings 2 and 2 of the two rolling bearings 1 and 1 are respectively fixed to the outer periphery of a shaft 6 and a preload is applied to the two rolling bearings 1 and 1.

[0294] The rolling bearing 1 comprises an outer ring 3 a having an outer raceway 3 a formed in the inner peripheral surface thereof, an inner ring 2 having an inner raceway 2 a formed in the outer peripheral surface thereof, a crown-shaped retainer 5 interposed between the outer and inner rings 3 and 2 in such a manner that it can be rotated with respect to the outer and inner rings 3 and 2, and a plurality of balls 4 rotatably held in a plurality of pockets 5 d formed in the crown-shaped retainer 5.

[0295] And, the outer peripheral edges 9 a of two circular-ring-shaped seal plates 9 (in the present embodiment, shield plates are used) (see FIG. 35A) are respectively secured to the inner peripheral surfaces of the two end portions of the outer ring 3. The two shield plates 9 and 9 not only prevent grease existing in the ball installation portions from leaking to the outside but also prevent dust floating in the outside from flowing into the ball installation portions.

[0296] The shield plate 9 is not limited to any specific structure but, instead of the shield plate 9, there can also be used a contact-type or non-contact-type seal. Also, in order to enhance the oscillation resistance of the product (ball bearing) in transit, the grease to be filled into the bearing 1 is filled into the grooves (that is, inner raceway 2 a and outer raceway 3 a) of the bearing 1.

[0297] Also, in the present invention, as the characteristic elements of the present invention, the crown-shaped retainer 5 to be incorporated into the bearing 1 is structured in the following manner. That is, the retainer 5 is structured such that the pocket diameter (Dp: see FIG. 53B) of the crown-shaped retainer 5 is set with respect to a ball diameter (Dw), namely, 1.050>Dp/Dw>1.005. The crown-shaped retainer 5 has an ordinary structure except for the ratio of Dp/Dw. That is, the crown-shaped retainer 5 comprises a circular-ring-shaped main portion 5 c and a plurality of pockets 5 d formed in the axial-direction one surface of the main portion 5 c, while the pockets 5 d are interposed between a pair of elastic pieces 5 e which are disposed spaced from each other in the axial-direction one surface of the main portion 5 c. For example, there can be properly selected a retainer of a ball guide type shown in FIGS. 53A and 53B, or a retainer of an inner/outer ring guide type including a projecting portion provided on the outer periphery or inner periphery thereof (which is disclosed in JP-A-10-159855).

[0298] Also, in the present embodiment, as the characteristic elements of the present invention, the pocket counter-opening sides 5 b and 5 b of the respective retainers 5 and 5 of the two bearings 1 and 1 are disposed opposed to each other; and, a preload is applied not only to the end faces 2 b and 2 b of the inner rings 2 and 2 situated on the pocket opening sides 5 a and 5 a of the retainers but also to the end faces 3 b and 3 b of the outer rings 3 and 3 situated on the pocket counter-opening sides 5 b and 5 b of the retainers.

[0299] According to the present embodiment, a spacer 7 is interposed between the outer rings 3 and 3 of the bearings 1 and 1, and a preload Fao is applied to the inner rings 2 and 2 from the retainer pocket opening sides 5 a and 5 a, so that the preload can be applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b (see FIG. 25).

[0300] In the bearing 1 with the thus-structured crown-shaped retainer 5 incorporated therein, by applying the preload not only to the end face 2 b of the inner ring 2 situated on the retainer pocket opening side 5 a but also to the end face 3 b of the outer ring 3 situated on the retainer pocket counter-opening side 5 b, it is possible to design a bearing apparatus which is low in dynamic friction torque and small in noises and vibrations.

[0301] By the way, the inner ring 2, outer ring 3, ball 4 and seal plate (seal or shield) 9 are not limited to any specific structures but they can be structured arbitrarily. Therefore, the detailed description thereof is omitted here. Also, the method for applying the preload and the quantity of the preload are not limited, that is, the optimum quantity of preload may be set according to cases.

[0302] Now, FIG. 26 shows a twenty-sixth embodiment of a bearing apparatus according to the present invention.

[0303] In the present embodiment, as the characteristic elements of the present invention that are different from the twenty-fifth embodiment, the pocket opening sides 5 a and 5 a of the respective retainers 5 and 5 of the two bearings 1 and 1 are disposed opposed to each other; and, a preload is applied not only to the end faces 2 c and 2 c of the inner rings 2 and 2 situated on the pocket opening sides 5 a and 5 a of the retainers 5 a and 5 a but also to the end faces 3 c and 3 c of the outer rings 3 and 3 situated on the pocket counter-opening sides 5 b and 5 b of the retainers 5 and 5.

[0304] According to the present embodiment, a spacer 7 is interposed between the inner rings 2 and 2 of the bearings 1 and 1, and a preload Fao is applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b, so that the preload can be applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b (see FIG. 26). By the way, the direction and method for applying the preload as well as the pocket diameter dimension of the retainer are similar to the twenty-fifth embodiment; and, the remaining structures of the inner rings 2, outer rings 3, rolling elements 4 and seal plates (seals or shields) 9 are not limited to any specific ones but they can be structured arbitrarily. Therefore, the structures of the previously described twenty-fifth embodiment are employed here and thus the detailed description thereof is omitted here.

[0305] Here, description will be given below of a fourth test conducted in order to confirm the effects of the present invention.

[0306] Bearing: inside diameter, 5 mm; outside diameter, 13 mm; and, width, 3 mm (corresponding to JIS 695).

[0307] Number or rotations: 10000 min⁻¹

[0308] Preload: 20N

[0309] Time: Vibrations and torque, values measured five minutes after start of rotation.

[0310] In the fourth test, while the ratio Dp/Dw between the pocket diameter (Dp) of the crown-shaped retainer 5 and ball diameter (Dw) was set in the range of 1.005-1.070, by changing the preload applying directions, the vibration amplitude (here, the retainer rotation component of the vibration) and dynamic friction torque were measured.

[0311]FIG. 34 shows the results of the fourth test. By the way, an A-direction preload shown in FIG. 34 expresses a preload (the present invention) which was applied not only to the retainer pocket opening side 5 a of the inner ring 2 but also to the retainer pocket counter-opening side 5 b of the outer ring 3; and, a B-direction preload expresses a preload (comparison example) which was applied not only to the retainer pocket counter-opening side 5 b of the inner ring 2 but also to the retainer pocket opening side 5 a of the outer ring 3. And, FIG. 35A shows a schematic view of the A-direction preload as the present invention, where as FIG. 35B shows a schematic view of the B-direction preload as the comparison example.

[0312] The fourth test results show that the dynamic friction torque of the bearing apparatus decreases as the ratio Dp/Dw increases and, on the other hand, the vibrations of the bearing apparatus increase as the ratio Dp/Dw increases.

[0313] However, both of the dynamic friction torque and vibrations do not vary uniformly but vary in an exponential curve manner. That is, 1.050>Dp/Dw>1.005 can be found as the range in which the dynamic friction torque and vibrations do not increase excessively.

[0314] Also, from the viewpoint of the vibrations, for example, a magnetic storage, which is represented by an HDD, has recently become very highly dense, while the number of tracks per inch is going to reach 75,000 TPI (Track Per Inch).

[0315] Here, in the case of 75,000 TPI, the width of the track is 0.33 μm/track and, in order to distinguish a piece of track information clearly from its adjoining track information when reading and writing a signal, it is the that the vibration of a magnetic disk must be controlled down to {fraction (1/30)} of the track width.

[0316] Therefore, there arises the need to control the vibration down to 0.01 μm. In case where this is applied to the vibration of the A-direction preload in FIG. 34, it is found that the ratio (Dp/Dw) must be set for 1.05 or less. On the other hand, referring to the preload applying direction, it can be seen clearly that the A-direction preload shown in FIG. 35A is smaller in both of the dynamic friction torque and vibrations.

[0317] From this, the following fact can be confirmed: that is, in case where not only the preload is applied from the retainer pocket opening side 5 a of the inner ring 2 and the retainer pocket counter-opening side 5 b of the outer ring 3 (the preload direction A shown in FIGS. 25, 26 and 35A) but also the ratio (Dp/Dw) of the pocket diameter (Dp) of the crown-shaped retainer 5 to the ball diameter (Dw) is set in the range of 1.005 to 1.050, the dynamic friction torque and vibrations can be made very excellent.

[0318] By the way, it is not preferable to set the ratio (Dp/Dw) at 1.005 or less. That is, in the case of the ratio (Dp/Dw) of 1.005 or less, when an error in manufacturing the crown-shaped retainer 5 is taken into account, there is a fear that the retainer pocket can restrict the balls.

[0319] Now, description will be given below of the preferred embodiments of a ball bearing and a bearing apparatus according to the present invention. By the way, the illustrated embodiments are just an example of the present invention and thus, of course, the present invention is not limited to the illustrated embodiments at all.

[0320]FIG. 36 shows a schematic section view of an embodiment of a ball bearing according to the present invention.

[0321] The ball bearing 1 comprises an inner ring 2 having an inner raceway 2 a formed in the outer periphery thereof, an outer ring 3 having an outer raceway 3 a formed in the inner periphery thereof, a plurality of rolling elements to be incorporated into between the inner raceway 2 a and outer raceway 3 a, and a crown-shaped retainer 5 for holding the rolling elements 4 at regular intervals.

[0322] Also, as the need arises, between the inner and outer rings 2 and 3 of the ball bearing 1, there may be interposed two seal rings (in the present embodiment, shield rings) 9. The structure of the seal ring 9 is not limited to any specific structure but the structure of the seal ring 9 can be changed without departing from the scope of the present invention. Also, in order to enhance the oscillation resistance of the product (ball bearing 1) in transit, a lubricant such as grease to be filled into the ball bearing 1 is filled into the raceways (that is, the inner raceway 2 a and outer raceway 3 a) of the ball bearing 1.

[0323] The crown-shaped retainer 5, for example, as shown in FIG. 37, comprises a circular-ring-shaped main portion 5 c and a plurality of pockets 5 d respectively formed in one surface of the main portion 5 c in the axial direction thereof; and, each of the pockets 5 d is interposed between a pair of pawls (which may also be referred to as elastic pieces) which are disposed in the axial-direction one surface of the main portion 5 c with a clearance between them. And, the ball bearing 1 according to the present invention is characterized in that, when the outer raceway shoulder position 3 d of the outer ring 3 is considered as the standard, the pawl height T of the retainer 5 is 20% or less of the diameter Da of the ball (rolling element) (that is, T≦20%×Da). The significance of such numerical definition will be discussed later in combination with the results of a fifth test (which will be described later).

[0324] Also, the ball bearing 1 according to the present invention is also characterized in that a preload is applied not only to the inner ring 2 situated on the pocket opening side 5 a of the retainer 5 but also to the outer ring 3 on the pocket counter-opening side 5 b of the retainer 5.

[0325] Now, FIG. 25 shows a twenty-seventh embodiment of a bearing apparatus according to a twelfth aspect of the present invention in which two ball bearings according to the previously described eleventh aspect of the present invention are respectively fixed to a shaft. Specifically, the present bearing apparatus comprises two rolling (ball) bearings 1 and 1 each having the above structure, while the two bearings 1 and 1 are combined together in such a manner that the inner rings 2 and 2 of the two bearings 1 and 1 are respectively fixed to a shaft 6, while a preload is applied to the two bearings 1 and 1.

[0326] More specifically, in the present embodiment, the pocket counter-opening sides 5 b and 5 b of the retainers 5 and 5 of the two bearings 1 and 1 are disposed opposed to each other and, between the outer rings 3 and 3 of the two bearings 1 and 1, there is interposed a spacer 7; and, by applying a preload Fao to the inner rings 2 and 2 from the pocket opening sides 5 a and 5 a of the retainers 5 and 5, the preload can be applied to the outer rings 3 and 3 from the pocket counter-opening sides 5 b and 5 b (see FIG. 25). By the way, the method for applying the preload is not limited to any specific method but it can be changed without departing from the scope of the present invention. Also, the quantity of the preload is not limited to any specific quantity but can be properly set at the optimum quantity according to cases.

[0327] With use of the two bearings each incorporating the crown-shaped retainer 5 therein, in case where a preload is applied not only to the inner ring end faces 2 b and 2 b situated on the retainer pocket opening sides 5 a and 5 a but also to the outer ring end faces 3 b and 3 b situated on the retainer pocket counter-opening sides 5 b and 5 b, there can be designed a bearing apparatus which is low in torque and is high in rotation accuracy.

[0328] Further, the grease G filled into the raceways of the bearings collects on the counter-contact-angle sides and, especially, due to the centrifugal force, the grease G collects on the outer ring sides. In case where, as described above, the preload is applied not only to the inner ring end faces 2 b on the retainer pocket opening sides 5 a but also to the outer ring end faces 3 b on the retainer pocket counter-opening sides 5 b, as the ball 4 is rotated, the grease G collecting on the counter-contact-angle sides, as shown in FIG. 36, moves to the retainer pawl 5 e sides in parallel to a contact angle line B (in FIG. 36, the moving direction of the grease G is shown by an arrow mark A). According to the present embodiment, since the pawl height T of each of the outer rings 3 with respect to the raceway shoulder position 3 d is set 20% or less of the ball diameter Da (T≦20%×Da), the scraping of the grease G can be controlled and the scraped grease G can be accumulated between the pawls 5 e and 5 e, which can provide proper supply of grease The above operation makes it possible to realize bearing specifications which can provide low torque variations, low torque and low vibrations. Also, the dust generation problem can be solved by using a magnetic fluid seal.

[0329] Now, FIG. 26 shows a twenty-eighth embodiment of a bearing apparatus according to the present invention.

[0330] The present embodiment has the following characteristic elements which are different from the twenty-seventh embodiment: that is, the pocket opening sides 5 a and 5 a of the respective retainers 5 and 5 of two bearings 1 and 1 are disposed opposed to each other; and, a preload is applied not only to the inner ring end faces 2 c and 2 c situated on the retainer pocket opening sides 5 a and Sa but also to the outer ring end faces 3 c and 3 c situated on the retainer pocket counter-opening sides 5 b and 5 b. According to the present embodiment, between the inner rings 2 and 2 of the two bearings 1 and 1, there is interposed a spacer 7 and a preload Fao is applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b, whereby the preload can be applied to the inner rings 2 and 2 from the retainer pocket opening sides 5 a and 5 a (see FIG. 26). The remaining structures of the inner rings 2, outer rings 3, rolling elements 4 and retainers 5 as well as the operation effects of the present bearing apparatus are similar to those of the previously described twenty-seventh embodiment and thus, by applying the description of the twenty-seventh embodiment, the detailed description thereof is omitted here.

[0331] By the way, in the present embodiment, description will be given below of a structure using two bearings 1 and 1 as a pair. However, the present invention is not limited to such combination of two bearings.

[0332] Also, in order to be able to apply the preload Fao to the inner ring 2 on the retainer pocket opening side 5 a, when assembling the bearing 1 to the shaft 6, it is necessary that the incorporating direction of the retainer 5 is known.

[0333] For this reason, in the ball bearing 1 according to the present embodiment, as shown in FIGS. 24A and 24B, between one end face 1 a and the other end face 1 b of the ball bearing 1 in the axial direction thereof (in FIG. 24A, in the right and left direction), there is provided meas (a distinctive arrangement) which allows the incorporating direction of the retainer 5 to be distinguished from the outside.

[0334] As the distinctive arrangement to be provided between the two end faces 1 a and 1 b, for example, there can be used the following arrangements.

[0335] That is, as shown in FIGS. 24A and 24B, marks 11 and 11 capable of distinguishing the retainer incorporating direction may be applied only to one end face 2 b and/or 3 b of one or both of the inner and outer rings 2 and 3.

[0336] These marks 11 and 11, for example, as shown in FIG. 24B, can be applied to the bearing inner ring end face 2 b and outer ring end face 3 b respectively situated on the retainer pocket opening side 5 a. In case where the marks 11 and 11 are applied to the bearing inner ring end face 2 b and outer ring end face 3 b on the retainer pocket opening side 5 a in this manner, the end face with these marks 11 and 11 applied thereto indicates the retainer pocket opening side 5 a. By the way, alternatively, the illustrated structure may be reversed; that is, the marks 11 may also be applied to the bearing inner ring end face 2 c and outer ring end face 3 c respectively situated on the pocket counter-opening side 5 b of the retainer 5. In this case, the end face with these marks 11 and 11 applied thereto indicates the incorporation start position side of the retainer 5 and thus, naturally, the end face with no such marks can be confirmed as the pocket opening side 5 a. In FIGS. 24A and 24B, “x” is shown as the mark but this is just an example of the mark: that is, the mark is not limited to “x” but the mark can be selected arbitrarily. The mark 11 may be engraved or may be formed in a plane shape or in a projecting shape; and, the number and position of marks can also be selected arbitrarily. Also, the mark 11 may also be provided on only one of the two seal rings 9.

[0337] Also, in case where the seal rings 9 and9 are made different in color or material from each other to thereby make a distinction between the two end sides of the bearing, the incorporating direction of the retainer 5 can also be distinguished from the outside. For example, the two seal rings 9 and 9 may be made different in color or pattern from each other; or, one of the seal rings 9 may be made of synthetic resin or rubber and the other seal ring 9 may be made of steel material. In this case as well, the incorporating direction of the retainer 5 can be distinguished from the outside. Also, when the seal ring is made of synthetic resin, in case where transparent synthetic resin is used as the synthetic resin, the retainer incorporating direction can be confirmed through the transparent seal ring.

[0338] Also, instead of mounting the seal rings 9 respectively on the two end faces of the bearing 1 as described above, the seal rings 9 may also be mounted on only one of the two end faces of the bearing 1. In this case as well, the incorporating direction of the retainer 5 can be distinguished from the outside. That is, in case where the seal rings 9 are mounted only on the bearing end face situated on the pocket counter-opening side 5 b of the retainer 5 or only on the bearing end face situated on the pocket opening side 5 d of the retainer 5, the side with the seal ring 9 mounted thereon provides the retainer pocket opening side 5 a (or, the retainer pocket counter-opening side 5 b), so that the incorporating direction of the retainer 5 can be distinguished easily.

[0339] Further, undulations such as notches may be formed in the axial-direction end edge portion(s) of one or both of the inner and outer rings 2 and 3 to thereby make a distinction between them. In this case as well, the incorporating direction of the retainer 5 can be distinguished.

[0340] Therefore, according to the present embodiment, an automatic machine for assembling a bearing to a spindle motor for HDD can also be structured such that, while distinguishing the incorporating direction of the retainer 5 through the undulations such as notches, it can assemble the bearing in a given direction.

[0341] In the process for manufacturing the rolling bearing with a seal, an operation to provide a distinctive arrangement between the two end faces of the rolling bearing according to the retainer incorporating direction can be carried out easily and positively without incurring any other special troublesome operation.

[0342] In the case of the above-structured ball bearing with a seal, since the retainer incorporating direction can be easily and positively distinguished from the outside, the assembling directions of the respective bearings can be controlled positively according to the retainer incorporating direction.

[0343] With use of the above-mentioned structure for the rolling bearing 1, because there can be provided various distinctive arrangements in the seal rings 9 of the bearing 1 or in the races (inner ring 2 and outer ring 3) of the bearing 1 which allow the incorporating direction of the retainer 5 to be distinguished from the outside, for example, even in the case of the bearing with the seal rings 9 and 9 mounted on the two end portions 1 a and 1 b thereof, the incorporating direction of the retainer 5 can be distinguished from the outside easily.

[0344] Thanks to this, the preload Fao can be applied simply and positively to the inner ring 2 situated on the retainer opening side 5 a, which makes it possible to reduce the rotation torque of the bearing apparatus and variations in such rotation torque as well as the vibrations of the bearing apparatus not synchronous with rotation of the bearing apparatus.

[0345] For example, according to the bearing apparatus shown in FIG. 25, in FIG. 25, the marks 11 shown in FIGS. 24A and 24B are applied, in the case of the axial-direction upper bearing 1, to the end faces (in FIG. 25, the upper end faces) 2 b and 3 b of the inner and outer rings 2 and 3 of the upper bearing 1 and, in the case of the axial-direction lower bearing 1, to the end faces (in FIG. 25, the lower end faces) 2 b and 3 b of the inner and outer rings 2 and 3 of the lower bearing 1; that is, the two bearings 1 are assembled together in such a manner that the marks 11 and 11 are not opposed to each other.

[0346] Also, according to the bearing apparatus shown in FIG. 26, in FIG. 26, the marks 11 shown in FIGS. 24A and 24B are applied, in the case of the axial-direction upper bearing 1, to the end faces (in FIG. 26, the lower end faces) 2 b and 3 b of the inner and outer rings 2 and 3 of the upper bearing 1 and, in the case of the axial-direction lower bearing 1, to the end faces (in FIG. 26, the upper end faces) 2 b and 3 b of the inner and outer rings 2 and 3 of the lower bearing 1; that is, the two bearings 1 are assembled together in such a manner that the marks 11 and 11 are opposed to each other.

[0347] Next, description will be given below of a fifth test conducted in order to confirm the effects of the present invention.

[0348] In the present test, a miniature ball bearing for information equipment having an inside diameter of 5 mm, an outside diameter of 13 mm and a width of 3 mm was assembled into an HDD/SPM apparatus (FIG. 29), and time series variations in the torque and NRRO of the two following structures were measured and compared. By the way, in the present test, the end face 2 b of the inner ring 2 in one bearing (in FIG. 29, the lower bearing) was butted against a stepped portion 6 a raised formed on one end side of the shaft 6 of the HDD/SPM apparatus; between the outer rings 3 and 3 of the two bearings 1 and 1, there were interposed the stepped portions 8 that were formed in the inside diameter surface of the housing; a weight or a spring force equal to a desired preload was applied to the end face 2 b of the inner ring 2 of the other bearing (in FIG. 25, the upper bearing) to thereby fix the inner ring 2 to the shaft 6 by adhesion. In this case, instead of adhesion, the inner ring 2 may also be fixed by pressure insertion.

[0349] Number of rotations: 7200 min⁻¹ (outer ring rotation)

[0350] Preload: Axial load 11.76N (1.2 kgf)

[0351] Time: 2 Hrs.

[0352] Here, a fifth test was conducted to confirm the effects of the retainer direction and preload direction according to the present invention. Referring to test samples, the bearing having the same specifications as described above was assembled into a related structure to thereby provide one test sample, while the same bearing is assembled into a structure according to the present invention to thereby provide the other test sample; and, the effects of the two test samples were compared.

[0353]FIGS. 29 and 30 show the results of the comparison fifth test. Specifically, FIG. 30 shows the results of the structure according to the present invention, whereas FIG. 29 shows the results of the related structure (in the respective figures, (a) shows the time series variations of the torque and (b) shows the time series variations of NRRO). These results show clearly that the structure according to the present invention is small in the torque and variations in the torque as well as in NRRO. When these results are compared with the results of the related structure, it can be confirmed that the structure according to the present invention is better in both torque and NRRO than the related bearing apparatus.

[0354] Next, a fifth test was conducted to confirm the effects of the present invention as to the position of the pawl 5 e of the crown-shaped retainer 5. When the height T of the pawl 5 e of the crown-shaped retainer 5 was 30%, 20%, 10%, 0%, −10%, and −20% of the ball diameter Da, the respective NRRO and torque were measured in a time series manner, and there were compared times that were taken for the time series measured NRRO values to go below the measurement initial values such that NRRO: ⅓ and torque: ½.

[0355] From the fifth test results, as shown in FIG. 38, it can be confirmed that, in the case of the pawl height T being 20% or less of the ball diameter Da, NRRO and torque are stabilized at an early stage and, in the case of the pawl height T being higher than 20% of the ball diameter Da, it takes time for NRRO and torque to stabilize. That is, it can be confirmed that, in order to stabilize NRRO and torque early, the pawl height T of the crown-shaped retainer 5 must be 20% or less of the ball diameter Da. Further, preferably, the pawl height T may be 0% or less and, from the viewpoint of rigidity, it may be −15% or less.

[0356] In the present embodiment, the shape of the pawl 5 e of the crown-shaped retainer 5 is not limited to any specific shape but the present invention can also apply to any pawl shape. For example, as shown in FIG. 39, it may be effective to cut away the leading end portions of the pawl 5 e obliquely. In FIG. 39, the broken-line portions show the cut-away portions.

[0357] Now, description will be given below of the preferred embodiments of a bearing apparatus according to the present invention with reference to the accompanying drawings. By the way, the illustrated embodiments are just an example of the present invention and thus the present invention is not limited to the illustrated embodiments at all.

[0358]FIG. 40 shows a twenty-ninth embodiment of a bearing apparatus according to the present invention.

[0359] The present bearing apparatus comprises two ball bearings 1 and 1, while the two ball bearings 1 and 1 are combined together in such a manner that the inner rings 2 and 2 of the two ball bearings 1 and 1 are respectively fixed to the outer periphery of a shaft 6 and a preload is applied to the two ball bearings 1 and 1.

[0360] The rolling (ball) bearing 1 comprises an outer ring 3 having an outer raceway 3 a formed in the inner peripheral surface thereof, an inner ring 2 having an inner raceway 2 a formed in the outer peripheral surface thereof, a crown-shaped retainer 5 interposed between the outer and inner rings 3 and 2 in such a manner that it can be rotated with respect to the outer and inner rings 3 and 2, and a plurality of balls 4 respectively rotatably held in a plurality of pockets 5 d formed in the crown-shaped retainer 5.

[0361] To the inner peripheral surfaces of the two end portions of the outer ring 3, there are secured the outer peripheral edges 9 a and 9 a of their associated circular-ring-shaped seal plates (in the present embodiment, shield plates) 9 and 9, respectively; and, the two shield plates 9 and 9 prevent grease existing in the above-mentioned ball installation portions from leaking to the outside or prevent dust floating in the outside from flowing into the ball installation portions.

[0362] By the way, the structure of the seal plate 9 is not limited to any specific structure but can be changed without departing from the scope of the present invention; and also, the seal plate 9 may also be provided as the need arises. Also, in order to enhance the oscillation resistance of the product (ball bearing) in transit, a lubricant to be filled into the ball bearing 1 is to be filled into the raceways (that is, the inner raceways 2 a and outer raceways 3 a) of the bearing 1.

[0363] The crown-shaped retainer 5, for example, as shown in FIG. 53A, comprises a circular-ring-shaped main portion 5 c and a plurality of pockets 5 d formed in one surface of the main portion 5 c in the axial direction thereof. And, each of the pockets 5 d is interposed between a pair of pawls (which are also referred to as elastic pieces) 5 e disposed in the axial-direction one surface of the main portion 5 c such that they are spaced from each other.

[0364] As described above, the present (rolling) ball bearing is not limited to any specific structure but employs an ordinary structure as a ball bearing. However, the present embodiment has the following characteristic elements of the present invention. That is, the pocket counter-opening sides 5 b and 5 b of the respective retainers 5 and 5 of the two bearings 1 and 1 are disposed opposed to each other; a preload is applied not only to the end faces 2 b and 2 b of the inner rings 2 and 2 situated on the retainer pocket opening sides 5 a and 5 a but also to the end faces 3 b and 3 b of the outer rings 3 and 3 situated on the retainer pocket counter-opening sides 5 b and 5 b; and, an initial contact angle between the ball and raceway surface is set at an angle of 15°. In other words, according to the present embodiment, there are interposed spacers 7 between the outer rings 3 and 3 of the two bearings 1 and 1; the preload Fao is applied to the inner ring end faces 2 b and 2 b situated on the retainer pocket opening sides Sa and 5 a, so that the preload is applied to the outer ring end faces 3 b and 3 b from the retainer pocket counter-opening sides 5 b and 5 b; and, the initial contact angle is set at an angle of 15°. The initial contact angle, as shown in sixth test results which will be discussed later, may be an angle of 5° or more and, preferably, it may be set in the range of 5 to 30°.

[0365] The structures of the inner rings 2, outer rings 3, balls 4 and seal plates (or, shield plates) 9 as well as the clearances of the bearings are not limited to any specific ones but can be selected arbitrarily and thus the detailed description thereof is omitted here.

[0366] Also, the method for applying the preload and the quantity of the preload are not limited to any specific ones but the quantity of the preload can be set at the optimum quantity according to cases.

[0367] According to the ball bearing 1 with the crown-shaped retainer 5, since the preload is applied not only to the inner ring end faces 2 b and 2 b situated on the retainer pocket opening sides 5 a and 5 a but also to the outer ring end faces 3 b and 3 b situated on the retainer pocket counter-opening sides 5 b and 5 b, and also since the initial contact angle is set at an angle of 15°, there can be designed a bearing apparatus which is low in dynamic friction torque and is small in variations in such dynamic friction torque.

[0368] Now, FIG. 41 shows a thirtieth embodiment of a bearing apparatus according to the present invention.

[0369] The present embodiment has the following characteristic elements of the present invention that are different from the twenty-ninth embodiment. That is, the pocket opening sides 5 a and 5 a of the respective retainers 5 and 5 of the two bearings 1 and 1 are disposed opposed to each other; and, a preload is applied not only to the end faces 2 c and 2 c of the inner rings 2 and 2 situated on the retainer pocket opening sides 5 a and 5 a but also to the end faces 3 c and 3 c of the outer rings 3 and 3 situated on the retainer pocket counter-opening sides 5 b and 5 b. The initial contact angle, similarly to the twenty-ninth embodiment, is set at an angle of 15°.

[0370] According to the present embodiment, there are interposed spacers 7 between the inner rings 2 and 2 of the two bearings 1 and 1; and, the preload Fao is applied to the outer rings 3 and 3 from the retainer pocket counter-opening sides 5 b and 5 b, so that the preload is applied to the inner rings 2 and 2 from the retainer pocket opening sides 5 a and 5 a (see FIG. 41).

[0371] By the way, the load applying method and direction as well as the pocket diameter dimension of the retainer 5 are similar to those of the twenty-ninth embodiment. Also, the remaining structures of the inner rings 2, outer rings 3, balls 4 and seal plates 9 as well as the operation effects of the present bearing apparatus are similar to those of the twenty-ninth embodiment. Therefore, by applying the description of the twenty-ninth embodiment, the detailed description thereof is omitted here.

[0372] Here, description will be given below of a sixth test conducted to confirm the effect of the present invention.

[0373] Bearing (which corresponds to JIS695): inside diameter, 5 mm; outside diameter, 13 mm; and width, 4 mm.

[0374] Number of rotations: 10000 min⁻¹

[0375] Preload: 20N

[0376] Time: dynamic friction torque values five minutes after rotation start were measured.

[0377] In the sixth test, while changing the initial contact angle in the range of 5 to 30° by changing the clearance of the bearing, the preload direction was changed and the dynamic friction torque was measured.

[0378]FIG. 42 shows the results of the above sixth test. By the way, FIGS. 43A and 43B are respectively schematic views which correspond to preload directions A and B shown in FIG. 42. Here, “A-direction preload” means a preload which, as in the twenty-ninth and thirtieth embodiments respectively shown in FIGS. 40 and 41, is applied from the portion of the inner ring 2 on the retainer pocket opening side 5 a and from the portion of the outer ring 3 on the retainer pocket counter-opening side 5 b; and, “B-direction preload” means a preload which, reversely to the A-direction preload, is applied from the portion of the inner ring 2 on the retainer pocket counter-opening side 5 b and from the portion of the outer ring 3 on the retainer pocket opening side 5 a.

[0379] The results of the sixth test show that, when the preload is applied in the B direction, as the initial contact angle decreases, the dynamic friction torque decreases. On the other hand, when the preload is applied in the A direction, in case where the initial contact angle is 10° or so, the dynamic friction torque is smaller than the A-direction preload; however, in case where the initial contact angle goes below this value, the dynamic friction torque increases suddenly and becomes almost the same as the B-direction preload. In the case of the initial contact angle of 5° or less, there is little difference between the A- and B-direction preloads.

[0380] That is, the initial contact angle may be set at 5° or more and, preferably, it may be set 7° or more where the dynamic friction torque provides a sufficiently low value; and, the preload direction may be the direction (A direction) shown in FIGS. 40 and 41.

[0381] By the way, in the present test, the initial contact angle is set up to 30°. However, in case where the initial contact angle is excessively large, there is a fear that the load of the ball occurring when the ball moves up onto the raceway surface can be lowered to thereby impair the intrinsic function of the bearing. Therefore, in case where the preload is large or in case where it can be assumed that not only the preload but also an axial-direction force are applied, the initial contact angle must be set at an angle not exceeding the angle at which the ball can move up onto the raceway surface. For example, in the case of the bearing corresponding to JIS695 used in the present test, preferably, the initial contact angle may be set at an angle of 20° or less.

[0382] Also, in the respective embodiments, there is employed a combination of two ball bearings. However, the number of ball bearings to be combined is not limited to two; for example, use of a single ball bearing can also provide a similar effect, and use of three or more ball bearings can also provide a similar effect.

[0383] Further, in the present invention, the preload direction and the incorporating direction of the retainer 5 provide important elements. In case where the seal plates 9 are previously mounted on the two end faces of the bearing, the incorporating direction of the retainer 5 cannot be distinguished from the outside. Therefore, in order to be able to confirm the incorporating direction of the retainer 5, as shown in FIGS. 24A and 24B, between the two end faces 1 a and 1 b of the bearing 1 in the axial direction thereof (in FIG. 24A, in the right and left direction), there is provided an arrangement (a distinctive arrangement) through which the incorporating direction of the retainer 5 can be distinguished.

[0384] As the typical arrangement to be provided between the two end faces 1 a and 1 b of the bearing 1, there can be employed the following arrangements.

[0385] That is, as shown in FIGS. 24A and 24B, marks 11 and 11 for indicating the incorporating direction of the retainer 5 may be applied only onto one end face 3 b and/or 3 b of the inner ring 2 and/or outer ring 3.

[0386] The marks 11 and 11 can be applied, for example, as shown in FIG. 24B, to the bearing inner ring end face 2 b and outer ring end face 3 b on the retainer pocket opening side 5 a. In case where the marks 11 and 11 are applied to the bearing inner ring end face 2 b and outer ring end face 3 b on the retainer pocket opening side 5 a in this manner, the end face with the marks 11 and 11 applied thereto indicates the retainer pocket opening side 5 a. By the way, the marks 11 can be provided reversely to the illustrated example. That is, the marks 11 can also be applied to the bearing inner ring end face 2 c and outer ring end face 3 c on the pocket counter-opening side 5 b of the retainer 5. In this case, the marks 11 indicate the incorporation start position side of the retainer 5 and thus the end face side with no marks 11 can be naturally confirmed as the retainer pocket opening side 5 a. In FIGS. 24A and 24B, “x” is shown as the mark but this is just an example of the mark: that is, the mark is not limited to “x” but the mark can be selected arbitrarily. The mark 11 may be engraved or may be formed in a plane shape or in a projecting shape; and, the number and position of marks can also be selected arbitrarily. Also, the mark 11 may also be provided on only one of the two seal rings 9.

[0387] Also, in case where the seal rings 9 and 9 are made different in color or material from each other to thereby make a distinction between the two end sides of the bearing, the incorporating direction of the retainer 5 can also be distinguished from the outside. For example, the two seal rings 9 and 9 may be made different in color or pattern from each other; or, one of the seal rings 9 may be made of synthetic resin or rubber and the other seal ring 9 may be made of steel material. In this case as well, the incorporating direction of the retainer 5 can be distinguished from the outside. Also, when the seal ring is made of synthetic resin, in case where transparent synthetic resin is used as the synthetic resin, the retainer incorporating direction can be confirmed through the transparent seal ring.

[0388] Also, instead of mounting the seal rings 9 respectively on the two end faces of the bearing 1 as described above, the seal rings 9 may also be mounted only on one of the two end faces of the bearing 1. In this case as well, the incorporating direction of the retainer 5 can be distinguished from the outside. That is, in case where the seal rings 9 are mounted only on the bearing end face situated on the pocket counter-opening side 5 b of the retainer 5 or only on the bearing end face situated on the pocket opening side 5 d of the retainer 5, the side with the seal ring 9 mounted thereon provides the retainer pocket opening side 5 a (or, the retainer pocket counter-opening side 5 b), so that the incorporating direction of the retainer 5 can be distinguished easily.

[0389] Further, undulations such as notches may be formed in the axial-direction end edge portion(s) of one or both of the inner and outer rings 2 and 3 to thereby make a distinction between them. In this case as well, the incorporating direction of the retainer 5 can be distinguished.

[0390] Therefore, with use of a bearing apparatus according to the present embodiment, an automatic machine for assembling a bearing to a spindle motor for HDD can also be structured such that, while distinguishing the incorporating direction of the retainer 5 through the undulations such as notches, it can assemble the bearing in a given direction.

[0391] In the process for manufacturing the rolling bearing with a seal, an operation to provide a distinctive arrangement between the two end faces of the rolling bearing according to the retainer incorporating direction can be carried out easily and positively without incurring any other special troublesome operation.

[0392] In the case of the above-structured ball bearing with a seal, since the retainer incorporating direction can be easily and positively distinguished from the outside, the assembling directions of the respective bearings can be controlled positively according to the retainer incorporating direction.

[0393] With use of the above-mentioned structure for the rolling bearing 1, because there can be provided various distinctive arrangements in the seal rings 9 of the bearing 1 or in the races (inner ring 2 and outer ring 3) of the bearing 1 which allow the incorporating direction of the retainer 5 to be distinguished from the outside, for example, even in the case of the bearing with the seal rings 9 and 9 mounted on the two end portions 1 a and 1 b thereof, the incorporating direction of the retainer 5 can be distinguished from the outside easily.

[0394] Thanks to this, the preload Fao can be applied simply and positively to the inner ring 2 situated on the retainer opening side 5 a, which makes it possible to reduce the rotation torque of the bearing apparatus and variations in such rotation torque as well as the vibrations of the bearing apparatus not synchronous with rotation of the bearing apparatus.

[0395] For example, according to the bearing apparatus shown in FIG. 40, in FIG. 40, the marks 11 shown in FIGS. 24A and 24B are applied, in the case of the axial-direction upper bearing 1, to the end faces (in FIG. 40, the upper end faces) 2 b and 3 c of the inner and outer rings 2 and 3 of the upper bearing 1 and, in the case of the axial-direction lower bearing 1, to the end faces (in FIG. 41, the lower end faces) 2 b and 3 c of the inner and outer rings 2 and 3 of the lower bearing 1; that is, the two bearings 1 are assembled together in such a manner that the marks 11 and 11 are not opposed to each other.

[0396] Also, according to the bearing apparatus shown in FIG. 41, in FIG. 41, the marks 11 shown in FIGS. 24A and 24B are applied, in the case of the axial-direction upper bearing 1, to the end faces (in FIG. 41, the lower end faces) 2 c and 3 b of the inner and outer rings 2 and 3 of the upper bearing 1 and, in the case of the axial-direction lower bearing 1, to the end faces (in FIG. 41, the upper end faces) 2 c and 3 b of the inner and outer rings 2 and 3 of the lower bearing 1; that is, the two bearings 1 are assembled together in such a manner that the marks 11 and 11 are opposed to each other.

[0397] According to the present invention, since it has the above-mentioned structure, even in case the grease, which has moved to the outer raceway when in rotation, collects in a large quantity, since the grease collects from the raceway portions on the counter-contact-angle side to the shoulder portions of the raceways, the distance between the grease and retainer is large and thus the grease is not involved so much with the rotation of the retainer, which makes it possible to settle the bearing apparatus at low torque. Also, even in case where the grease collecting in the outer raceways is involved with the rotation of the ball, since the grease is scraped in the vicinity of the pawl leading end portion of the retainer and is held and settled between the pawls respectively interposed between the retainer pockets, the grease is not stirred so much, which provides an effect that the bearing apparatus can be made to settle at low torque. Thus, according to the present invention, there can be provided a bearing apparatus which is small in rotation torque and in variations in such rotation torque as well as is high in rotation accuracy.

[0398] As has been described heretofore, according to the present invention, since it is structured in the above-mentioned manner and thus the incorporating direction of the retainer can be distinguished from the outside simply and positively, the assembling directions of the respective bearings can be controlled positively according to the incorporating direction of the retainers. Therefore, in the case of a bearing apparatus incorporating the present bearings into the shaft, the preload can be applied to the inner rings on the retainer opening sides easily and positively, which makes it possible to reduce the rotation torque of the bearing apparatus and variations in such rotation torque as well as the vibrations of the bearing apparatus that are not synchronous with the rotation thereof.

[0399] According to the present invention, due to the above-described structure, there can be realized a bearing apparatus which is high in rotation accuracy, is low in both rotation torque and the variations of such rotation torque, and is able to control an increase in the temperature and the friction thereof for a long period of time. Use of the bearing apparatus having a structure according to the present invention not only can reduce the dynamic friction torque but also can prevent harmful noises and vibrations possibly caused by poor lubrication. This can enhance the performance of various rotary equipment incorporating the present bearing apparatus as well as can save the energy of such rotary equipment.

[0400] According to the present invention, since the ratio Dp/Dw of the pocket diameter (Dp) of the retainer to the ball diameter (Dw) is set such that 1.050>Dp/Dw>1.005, the movement of the retainer can be restricted, which can reduce the noises and vibrations of the bearing apparatus that could be otherwise generated due to the vibrations of the retainer. Also, because the preload is applied not only to the portion of the inner ring situated on the retainer pocket opening side but also to the portion of the outer ring on the retainer pocket counter-opening side, an increase in the dynamic friction torque of the bearing apparatus can be prevented.

[0401] Therefore, according to the present invention, due to the above two advantages, there can be provided a bearing apparatus which is very excellent in both of the dynamic friction torque and vibrations thereof.

[0402] According to the present invention, since the preload is applied not only to the inner ring on the retainer pocket opening side but also to the outer ring on the retainer pocket counter-opening side, the grease collects on the counter-contact-angle and, as the ball rotates, the grease moves to the retainer pawl side in parallel to the contact angle. Also, according to the present invention, by setting the pawl height for 20% or less of the outer raceway shoulder position, the scraping of the grease can be controlled, which makes it possible to supply the grease properly.

[0403] The above operations can realize such bearing specifications that can provide low torque variations, low torque and low vibrations.

[0404] As the bearing apparatus rotates, the grease existing in the interior portion of the bearing is caused to move; and, in case where a preload is applied to the bearing, the movement of the grease is made uneven on the right and left sides in the axial direction of the bearing. That is, it is known that the grease collects on the counter-contact side of the ball with respect to the inner ring or outer ring. According to the present invention, since the preload is applied not only to the portion of the inner ring on the retainer pocket opening side but also to the portion of the outer ring on the retainer pocket counter-opening side, and also since the initial contact angle is set at an angle of 5°, the moved grease is hard to accumulate on the outer ring inside diameter side which is situated on the retainer back surface side and is small in space capacity, so that resistance due to stirring of the grease is hard to occur between the outer ring inside diameter side and the retainer-back-surface-side outside diameter side. This can prevent an increase in the dynamic friction torque of the present bearing apparatus. 

What is claimed is:
 1. A bearing apparatus comprising a bearing fixed to a shaft, the bearing including: an outer ring having an outer raceway formed in an inner peripheral surface thereof; an inner ring having an inner raceway formed in an outer peripheral surface thereof; a crown-shaped retainer interposed between the outer and inner rings so as to be rotated with respect to the outer and inner rings; and a plurality of balls rotatably held in a plurality of pockets formed in the crown-shaped retainer, wherein a preload is applied to an retainer opening side of the inner ring of the bearing and an retainer counter-opening side of the outer ring of the bearing.
 2. A bearing apparatus comprising two bearings fixed to a shaft, each bearing including: an outer ring having an outer raceway formed in an inner peripheral surface thereof; an inner ring having an inner raceway formed in an outer peripheral surface thereof; a crown-shaped retainer interposed between the outer and inner rings so as to be rotated with respect to the outer and inner rings; and a plurality of balls rotatably held in a plurality of pockets formed in the crown-shaped retainer, wherein a preload is applied to the retainer opening sides of the respective inner rings of the two bearings and the retainer counter-opening sides of the respective outer rings of the two bearings.
 3. The bearing apparatus as set forth in claim 2, wherein the respective retainers of the two bearings are incorporated in such a manner that the pocket counter-opening sides of the retainers are opposed to each other.
 4. The bearing apparatus as set forth in claim 2, wherein the respective retainers of the two bearings are incorporated in such a manner that the pocket opening sides of the retainers are opposed to each other.
 5. A bearing apparatus comprising two bearings structured such that a preload is applied to respective outer rings of the two bearings by a spring interposed between the respective outer rings in a direction to separate the outer rings from each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket counter-opening sides of the retainer are opposed to each other.
 6. A bearing apparatus comprising two bearings structured such that a preload is applied to respective outer rings of the two bearings in a direction to approach the outer rings each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket opening sides of the retainers are opposed to each other.
 7. A bearing apparatus comprising two bearings structured such that a preload is applied to respective inner rings of the two bearings in a direction to approach the inner rings each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket counter-opening sides of the retainers are opposed to each other.
 8. A bearing apparatus comprising two bearings structured such that a preload is applied to respective inner rings of the two bearings by a spring interposed between the respective inner rings in a direction to separate the inner rings from each other, wherein crown-shaped retainers of the two bearings are incorporated in such a manner that respective pocket opening sides of the retainers are opposed to each other.
 9. The bearing apparatus as set forth in claim 5, further comprising a shaft fixing the two bearings, wherein the shaft includes a double row raceway so as to receive rolling elements of the two bearings.
 10. The bearing apparatus as set forth in claim 5, further comprising a shaft fixed to the bearing and an inner ring, wherein the shaft includes a raceway formed in one side thereof so as to receive rolling elements of one of the two bearings, whereas the inner ring is fixed to the other side of the shaft so as to receive rolling elements of the other of the two bearings.
 11. The bearing apparatus as set forth in claim 5, wherein a spring is interposed between the outer rings of the two bearings.
 12. The bearing apparatus as set forth in claim 5, wherein a raceway for balls is formed at least in a portion of the shaft or a housing.
 13. The bearing apparatus as set forth in claim 1, wherein the bearing apparatus is of an outer ring rotation type or an inner ring rotation type.
 14. The bearing apparatus as set forth in claim 1, wherein an indicating arrangement allowing the incorporating direction of the retainer to be distinguished is provided on at least one of one end face and the other end face of the bearing apparatus in the axial direction thereof.
 15. A rolling bearing comprising: an inner ring having an inner raceway formed in an outer peripheral surface thereof; an outer ring having an outer raceway formed in an inner peripheral surface thereof; a plurality of rolling elements rotatably interposed between the inner raceway and the outer raceway; a crown-shaped retainer for holding the rolling elements at regular intervals; and, a seal ring interposed between the inner and outer rings for sealing grease or lubricating oil filled into a bearing space or for preventing dust from being generated to the outside, wherein an indicating arrangement allowing the incorporating direction of the retainer to be distinguished is provided on at least one of one end face and the other end face of the bearing in the axial direction thereof.
 16. The rolling bearing as set forth in claim 15, wherein the indicating arrangement is a mark provided on either of the one end face or the other end face of the bearing in the axial direction thereof.
 17. The rolling bearing as set forth in claim 16, wherein the mark includes a toothing.
 18. The rolling bearing as set forth in claim 15, wherein the indicating arrangement is seal ring disposed on either of the one end face or the other end face of the bearing in the axial direction thereof.
 19. The rolling bearing as set forth in claim 15, wherein the indicating arrangements are seal rings which are respectively disposed on both of the one end face and the other end face of the bearing in the axial direction thereof and differ in color from each other.
 20. The bearing apparatus, wherein a bearing as set forth in claim 15 is fixed to a shaft and a preload is applied to a retainer opening side of the inner ring and a retainer counter-opening side of the outer ring.
 21. The bearing apparatus structured as set forth in claim 1, wherein the crown-shaped retainer has at least a rolling element sliding contact surface formed as a rough surface.
 22. The bearing apparatus structured as set forth in claim 2 wherein the crown-shaped retainers have at least a rolling element sliding contact surface formed as a rough surface.
 23. The bearing apparatus as set forth in claim 1, wherein a ratio Dp/Dw of a pocket diameter (Dp) of the retainer to a diameter of the ball (Dw) is set such that 1.050>Dp/Dw>1.005.
 24. The bearing apparatus as set forth in claim 2, wherein a ratio Dp/Dw of a pocket diameter (Dp) of the retainer to the diameter of the ball (Dw) is set such that 1.050>Dp/Dw>1.005.
 25. A ball bearing, comprising: an inner ring having an inner raceway formed in an outer peripheral surface thereof; an outer ring having an outer raceway formed in an inner peripheral surface thereof; a plurality of balls rotatably incorporated between the inner raceway and the outer raceway; and, a crown-shaped retainer for holding the balls at regular intervals, wherein a preload is applied to a pocket opening side of the inner ring of the retainer and a pocket counter-opening side of the outer ring of the retainer, and a pawl height T of the retainer is set 20% or less of the diameter Da of the ball (T≦20%×Da) with a shoulder position of the raceway of the outer ring as the standard.
 26. The ball bearing as set forth in claim 25, wherein an indicating arrangement allowing the incorporating direction of the retainer to be distinguished is provided on the two end faces of the ball bearing in the axial direction thereof.
 27. The bearing apparatus, wherein a ball bearing as set forth in claim 25 is incorporated into a shaft.
 28. The bearing apparatus as set forth in claim 1, wherein an initial contact angle between the ball and raceway surface of the raceway is set at an angle of 5° or more.
 29. The bearing apparatus as set forth in claim 28, wherein the two bearings are fixed to a shaft and the retainers of the two ball bearings are incorporated in such a manner that respective pocket counter-opening sides of the retainers are opposed to each other.
 30. The bearing apparatus as set forth in claim 28, wherein two ball bearings are fixed to a shaft and the retainers of the two ball bearings are incorporated in such a manner that respective pocket opening sides of the retainer are opposed to each other.
 31. The bearing apparatus as set forth in claim 28, wherein two seal plates are respectively disposed on the two end portions of the bearing in the axial direction thereof, and indicating arrangements allowing the incorporating direction of the retainer to be distinguished are provided on the two end portions of the bearing in the axial direction thereof and differ in color from each other. 